"Did not the Abbe F-M say: 'Lost is that man who sees a beautiful woman descending a noble staircase', and were not both these ingredients here, and ready to her hand? What else but a staircase could so perfectly set off the jewel she had made of Elfine?"
A character who has been presented to the audience as not particularly attractive cleans up, puts on nice clothes (or fancy clothes) and is suddenly stunningly attractive.
If it's a female, she may be originally be dowdy, unfashionable, a Tomboy or Wrench Wench, or simply not particularly attentive to her appearance. If it's a male character, he may be slovenly or sloppy. Either sex may be impoverished and therefore shabby in their normal appearance.
For non-native English speakers (or anyone who's confused), the trope name refers to the subject cleaning herself nicely — all prettied up for admiration.
Every adaptation of "Cinderella" ever has this moment as the abused scullery maid arrives at the ball with her Fairy Godmother powered ballgown. Possibly the Trope Maker.
Wrench Wenches are likely to have at least one scene like this. Tomboys and The Lad-ette also often have a moment like this — often tagged with a "Hey, I guess you really are a girl." This happens to the Undercover Model for work-related reasons.
Sister Trope to Beautiful All Along, Princess for a Day, Hollywood Homely and Bathe Her and Bring Her to Me. Occasionally involves a Pimped-Out Dress, but regular clothing will do. May be part of a Rags to Royalty situation. Sometimes overlaps with She Is All Grown Up. Contrast Unkempt Beauty, where she doesn't need to be cleaned up to look nice. Be aware of the Unnecessary Makeover where this trope doesn't work for the audience.
In Ranma ½, Akane gets Ranma but good twice, at the start and conclusion of the final story arc, when he sees her in a wedding kimono (first instance) and then in a Western-style wedding dress. Of course, she dresses up in fancy dresses whenever she can and usually does look pretty good, it's just that those two are the most prominent.
Also Ukyō in the Episode "Ukyō's Skirt, The Great Girly-Girl Gambit". Ukyō looks so stunning in a Fūrinkan girl's uniform that Kunō promptly decides to start courting her as well as Akane and "the pigtailed girl". Even Ranma only recognizes her because she's still carrying her giant spatula. Unfortunately for her, while all of the other guys at school wanted to date her, Ranma still didn't seem to get that what she wanted was to try and give their relationship a boost. Between that, and the fact it ended up in a contest where Ranma got beaten up by all of the other guys, she stopped wearing it out of remorse. She does occasionally dress up in more feminine garb, though the series has something of a Limited Wardrobe for her. She only wears the girl's uniform one other time, in her final appearance, and lampshades it in the original Japanese.
A male example occurs with Ranma, in a brief storyline in which Kodachi brings him as her date, to be compared to her rival's date. When said rival sees Ranma for the first time, he'd just been run over by a herd of cows and hardly looked his best. When he shows up at the actual date, cleaned up and looking awesome in a suit, the rival actually is impressed.
In the same arc, Akane becomes very offended when the rival insults Ranma. So, she helps make him look handsome for the date and mentally lampshades this trope while doing it.
Akane: I'll show her! When you dress Ranma up, he can be plenty cool!
Misty of Pokémon fame has done this from time to time. The infamous example of her wearing a kimono at the Summer Festival and actually rendering Ash speechless comes to mind.
Also, in one episode, Ash and Company met a girl who dresses and acts tough. At the end of the episode, when she invoked the trope, Brock reacted the way he usually does around beautiful girls, which prompted her into resuming her boyishness.
Kaname of Full Metal Panic! does this to Sōsuke while posing as an older, married, and sexually frustrated woman. It works amazingly.
She also pulls it with a kimono, shocking everyone.
Nadja Applefield from Ashita no Nadja embodies the trope whether dolled up via Leonardo and Thierry or wearing her Gorgeous Period Dress inherited from her Missing Mom. When said gown is destroyed by Rosemary, with help of Grandma Anna Nadja sews the intact top part into a new dress.
Continually subverted in The Wallflower — whenever the guys trick/force Sunako-chan into some proper clothes, Kyohei knows she's still the same person, and is (frustratingly) not quite cognisant of any attraction to her no matter how good she looks.
Even Amy Rose has done this on Sonic X, complete with the reaction from Sonic himself.
Subverted in Code Geass, where Nina Einstein is all dressed up in the pre-wedding celebration but is still much more confident at work as a scientist, which is demonstrated by comparison to matter. However, played straight with Milly Ashford on the same occasion and Cecile Croomy earlier. Absolute Cleavage indeed. Enforced on Kallen, who was particularly unwilling to get out of her pilot suit, but her Britannian captors insisted.
Akane-iro ni Somaru Saka uses this. All of the girls dress up and appear, getting a vague response from the main character. Then his sister shows up (late to the entrance) and he's dumbfounded. She's squicked by this, and he's berated by his fiancée (part of the first group).
In Powerpuff Girls Z, Kaoru/Buttercup gets her hair done and is dressed up nicely in the episode where she gets a crush on a guy with big muscles. She looks so different that the Professor and his son Ken didn't even recognize her. Momoko/Blossom and Miyako/Bubbles even managed to up it to eleven when they taught Kaoru manners.
Ouran High School Host Club's Haruhi cleans up nicely in the first chapter/episode going from frumpy and disheveled to a Bifauxnen. She's also dolled up during the Christmas ball to help get two fiancés back together, complete with a wig, dress, and makeup.
She complains about it, though, stating that her face feels heavy with all the makeup, and that it's hard to walk in the heels the boys gave her.
Louise Halevy from Gundam 00 puts on a nice pink kimono while visiting Japan. In the second season, she makes a really beautiful Elegant Gothic Lolita during a ball.
Tieria Erde not only dresses up really nicely for the same second season party, but mixes this with Wholesome Crossdresser.
Setsuna also cleaned up nicely in that same ball. Seeing him in a black suit was a very, very nice surprise.
In Record of Lodoss War Deedlit, wearing an extravagant white gown, walks down the stairs with Parn, who is having a LOT of trouble looking her in the eye. Subverted slightly as he spends most of the ball ignoring her advances and swooningover a famous hero.
And Deedo is so uncomfortable that she whines quite a bit at first, too.
Deedlit: Ah, this dress is so tight! Seriously, I don't know how you court ladies can wear these things ever day...
During the Greece Arc of Hayate the Combat Butler, Hayate winds up trying to pay back Hinagiku to show his appreciation for all her help. To do so he takes her out to a very fancy restaurant and tries very hard to put aside his troubling plot-related thoughts to ensure that she has a wonderful evening. He needn't have bothered as Hinagiku showed up a moment later wearing an elegant dress and looking literally stunning. As in Hayate's thoughts just stopped and he wound up staring at herfor a few minutes until she brought him back to reality.
Oscar in Rose of Versailles. She dressed like a man every day of her life, except one, at a ball, where she decided to go as a woman, in order to impress Fersen. It will work in a kind of way, but before it worked even more on her manservant and future lover André. The idea of Oscar in dress made him furious in manga, burst into laughter in anime... but in both, he stopped and looked amazed when Oscar showed up at the top of stairs in her white odalisque dress. And so were the guests at the ball later.
Kimi ni Todoke: normally Sawako's look wavers between scary or rather plain (except when she smiles from the heart). After a surprise makeover and a butterfly hairclip from Yano and Chizu, though, she broke the pretty barrier.
In Yotsuba&!, even rival Man Child Jumbo is impressed with Miura's traditional dress and performance at the autumn matsuri.
Kakeru from Area no Kishi notices this when he reunites with childhood friend Seven. She appears far more feminine than he remembered from their days in elementary school.
City Hunter: Kaori has sometimes put on a long wig and fooled her partner Ryo Saeba. In episode 137, an old friend of her buy Kaori fashionable clothes, and, with her wig, starts successfully dating Ryo at night. "Cinderella" was even the French title.
In HeartCatch Pretty Cure! episode 23, everyone's got their eyes on Itsuki after she first transforms into Cure Sunshine and later, when she first debuts in female clothing during the fashion club's trip in episode 25.
Miranda Lotto in D.Gray-Man. It was a shock for most readers when they saw her for the first time. Only for Miranda to become like this after she gained her Innocence and self-confidence for the first time in her life.
Happens during a Fancy Dinner scene in GUN×SWORD, with Wendy borrowing a fancy dress, taking her hair out of pigtails, and using makeup. Her dinner companion doesn't even recognize her at first. In context, his surprise may have a lot to do with the fact that she looks older—like a young woman rather than a child—than she does in her usual clothing.
Used in a somewhat weird way in the seventh Detective Conan movie. When Kazuha and Heiji were little, they visited Kazuha's family in Kyoto. Little Heiji ran off to a temple, and while waiting for him little Kazuha was dolled up in a kimono and got her hair done by her relatives. Little Heiji then saw her playing under the Cherry Blossoms, but didn't recognize her... and "that girl from Kyoto" remained in his memory as "his first love". Since the movie had a subplot in which Heiji was searching for the anonymous girl he once liked, it means Kazuha was jealous of... her dolled up little girl self. And Heiji didn't find out until the end of the movie.
Koala in One Piece was found by Fisher Tiger's crew, starting out like this◊, understandable since she was previously a slave. After spending some time with them, she looked like this◊. Hatchan even lampshaded how she has changed.
Faye from Cowboy Bebop is not a slouch in the looks department to start with, being Miss Fanservice for the show. But when circumstances in "Ballad Of Fallen Angels" call for her to drop her usual trashy outfit and do up not only her hair but also makeup and wardrobe to pass for a high-class opera patron, the effect on her is impressive. Too bad the Big Bad was waiting for her with a bunch of goons anyway.
In the first chapter of Rurouni Kenshin, Kenshin remarked how different Kaoru looked in her formal, feminine kimino compared to when they first met and she was wearing her scruffy dojo uniform.
Used in Rapunzel's Revenge, by Shannon and Dean Hale, illustrated by Nathan Hale (no relation). It's a graphic novel that sets the fairy tale "Rapunzel" in the American Southwest, and turns the title character into a hair-lassoing cowgirl.
Yoko Tsuno isn't afraid to dress up in a kimono once when she's invited to have dinner in a German castle, much to the surprise of everyone who sees her ("A kimono! In my castle! This is definitely something to celebrate for!", says their host). She also dolls up when she and her partners spent the night in a Scottish castle, and later spends a whole chase scene in a dress.
Strangers in Paradise's Katchoo says this to Detective Walsh (and he to her) when he goes undercover to help her bust Darcy. The normally tomboyish and disheveled Katchoo is wearing a fancy evening dress and makeup.
Inverted in the early Post-CrisisWonder Woman, Mynda Mayer, publicist extraordinaire, first appears in a sleazy dress and jewelry when she comes to Julia Kapatelis' residence to talk turkey with the new superhero. After being told to take a hike by the Greek professor as a cheap opportunist, Mayer doesn't give up and asks for a meeting in her office. Princess Diana and Ms. Kapatelis decide to come to stop her harassment, and are stunned to see the publicist in plain casual clothes and pants with far more subtle makeup and thus looking cute as a button.
Erstwhile demonstrates this trope while telling All-Fur, when the princess changes from her scruffy appearance to nice clothing for the ball. See it here.
Hawkman is very much capable of this on the rare occasion he is out of costume.
A central part of the "Persecuted Heroine" fairy tale type. This falls into two types:
Joseph Jacobs's "Tattercoats" also is a variant of the Persecuted Heroine, but unusually enough, the prince falls in love with her when she's wearing her tatters; she is cleaned up only at the end to convince his father and the court that she is suitable to marry her guy.
In another version of the tale, the prince agrees to marry her while she's in tatters but is confused as to why she goes around riding a goat and dressed in rags, while carrying a wooden spoon and with her face always dirty. With each question he has about her appearance (her mount, her clothing, her face, and her spoon), she replies that she only keeps those things because she wants to, and shows him that she is able to turn them into more beautiful things (a white horse, a gorgeous dress, a clean face, and a wand) should she desire. The prince gradually catches on and at the end, he doesn't even ask about the spoon, already knowing why she carries it.
Also used in the Japanese tale "Hanako's big hat". The heroine is a Fallen Princess who hides her Memento MacGuffin (a small chest with a scroll that proves her heritage) under a huge straw hat, which she wears 24/7 and refuses to take off in public. She is taken in as a maid by a high-class samurai clan, and when the eldest son falls for her, she has to clean up nicely to be accepted by her beau's family and prove who she truly is.
The heroine of Rebecca attempts to pull this off twice and both times it backfires horribly. The first time she dresses up in a stylish dress and does herself up to look like a woman on the cover of a magazine, which ends up freaking Maxim out. The second time is even worse when a costume ball comes around and she is tricked into dressing up as Maxim's dead wife.
In a Gender Flipped variant, in "Bearskin", when the hero, appalling shaggy, filthy and ragged, but rich, rescues a man from financial distress, the man promises that he may marry one of his daughters. Only the youngest is willing. However, his appearance stemmed from a Deal with the Devil, and that being over, He Cleans Up Nicely and formally arrives at their house as a wooer — or, in some variants, at his own wedding. Somewhat subverted, in that while the older sisters are impressed, the youngest, being the sort who would marry a hideous man to redeem her father's promise, ignores him until he proves that handsome as he is, he is still the same man whom she promised to marry.
Tanya Mousekewitz gets this kind of effect in An American Tail: Fievel Goes West after a makeover from Miss Kitty. Even the cats in the saloon take notice.
A variation in Tangled: Rapunzel's clothing doesn't change, but when Flynn gets four little girls to fix up her hair so it doesn't drag on the ground while they're touring the kingdom, Rapunzel ends up looking even cuter than before. Flynn's face when he sees the final result has the name of this trope written all over it.
Over the Hedge has a little makeover scene for Stella who, with a haircut and comb run through her fur, looks really pretty. For a skunk.
Mulan looks quite nice in her matchmaker ceremony dress. A more downplayed version appears in the climax where she appears wearing a dress again.
In Looney Tunes: Back in Action, Bugs presses a button in Damian Drake's car that dresses him and Kate in formal; attire. "Eh, you clean up nice, kid."
Wreck-It Ralph has Vanellope Von Schweetz transformed into a princess after crossing the finish line, looking quite adorable. Subverted as she prefers her regular clothes (no slouch in the cute department there, either).
Ralph:So...this is what you were all along. A princess.
Vanellope:Aw, come on, Ralph. What are you talkin' about? This isn't me...(glitches out of the princess get-up in to her regular clothes) This is me!
The Incredibles: A minor one with Violet Parr. At first, she wears baggy clothing and her hair is covering most of her face. After her Adrenaline Makeover, the last few scenes show her wearing fitting clothes and her hair is pulled back, making her look very pretty. Her crush comments on her new look, saying she looks different.
"I feel different. Is different okay?"
Tiana in The Princess and the Frog. In a variation, it's her friend Charlotte who expresses this. It also happens near the beginning of the movie. Tiana had previously only worn her work clothes.
Pocahontas didn't get one in her first movie but got two scenes in the sequel. The first was Played for Laughs as she walked into John Rolfe's room asking "how do I look?" - not realising she's only wearing undergarments. The second time is a straighter example as she descends the staircase in a ballgown.
Elsa in Frozen. In her case, it's her sister Anna who expresses this when she sees Elsa in her Snow Queen outfit for the first time.
Anna: Woah, Elsa, you look... different. It's a good different!
Film — Live Action
The non-canoncal The Dukes of Hazzard: The Beginning, where Daisy is a mousy, nerdy, timid little girl … until the day she puts on a pair of tight cutoff jeans, wearing a shirt tied to show her midriff and lets her hair down – and there you have a stunningly, ravishing, eye-candy hot-hot-hottie!
In the 2008 Japanese film Ichi, hapless samurai Toma meets the title character — a blind swordswoman — when she is in a goze's customary rags. When she's called to play for the local yakuza boss to celebrate Toma's hiring as a bodyguard, though, he is visibly stunned by how she looks in a kimono.
In Enchanted, the example is recursive. Giselle shows up at the ball (with Edward in tow) in this fashion. Funnily enough, the ball is an "old fashioned fancy dress" kind, involving clothing of the sort Giselle's been wearing for the whole movie — except now she shows up in a fairly simple modern-day dress. Robert still gets distracted away from his date Nancy, who is also dressed up fancily. The reason for Giselle's very striking effect is that she suddenly looks like a grown woman instead of a little girl playing dress-up with the Disney Princess dresses she'd worn until then.
Used retroactively in the book and The Film of the BookHarry Potter and the Goblet of Fire. In the book, Harry wonders who that pretty girl in a blue dress on Victor Krum's arm is, and nearly falls over when he realizes it's Hermione; Ron has an even worse reaction. Used straight, however, in the movie (because nobody in the audience could ever fail to recognize Emma Watson).
According to the extras in the DVD release, that was one of the hardest scenes for Daniel Radcliffe and Rupert Grint to get right, because although Ron and Harry had never seen Hermione all dolled up before, they had seen Emma done up to the nines on many occasions.
In Titanic Rose DeWitt Bukater descends the grand staircase of the RMS Titanic, drawing the obligatory wide-eyed expression from Jack Dawson. However, most of their fellow passengers' comments are focused on the fact it's Jack who cleans up nicely. Molly even says "You shine up like a new penny!"
Not to mention that Rose was wearing a rather pretty dress to dinner the night before. Seeing her dressed up would be a frequent event.
The title character from Carrie. In the 70s film it's alluded to early on when Miss Collins suggests things she could do to her appearance for the prom. In the 2002 TV movie one of the girls immediately compliments Carrie on her ass.
My Fair Lady has this moment for Eliza just before the ball, when she comes downstairs from her room and Higgins sees her in her gown for the first time.
Near the end of Quest for Camelot when Kayley steps into the room in her white dress. Her love interest is blind, however, so we don't get a reaction shot out of him.
The entire point of the movie Miss Congeniality. The scene where Gracie originally walks out of the hangar in a tight short knit dress with her hair up and makeup on, has all of her fellow FBI agents standing there with their jaws dropping.
Subverted somewhat when she stumbles on her heels and falls on her face immediately afterwards.
In an inversion of the trope, Australia has the male lead follow the trope nearly to the letter at a charity ball.
Inverted also in The Mummy after Rick O'Connell is rescued from the gallows. His shiny reappearance is nicely timed to Evelyn's rant about what a filthy, rude, complete scoundrel he is.
Evie herself gets a moment like this; before they go on their expedition we are used to seeing her in dowdy and plain librarian's clothes, but after they escape from the ship Evie appears wearing an Bedouin-inspired black dress and veil. Which certainly made Rick's eyes widen.
In the pee-wee football themed movie Little Giants, Becky "Icebox" O'Shea (a girl who plays halfback) falls in love with the team's quarterback and decides to go be a cheerleader instead, cleaning up nicely in the process. Of course, since the quarterback liked the girl who played halfback as opposed to a cheerleader, she un-cleans and wins the big game instead.
Happens in Bend It Like Beckham, when the girls are in Germany and Jessminder has nothing to wear for the party.
Inverted by Michelle Rodriguez in whatever movie she does; the dirtier she gets, the hotter she is.
Steven Spielberg's Always. Holly Hunter's character is a pilot and dispatcher who always dresses in dirty overalls. Her boyfriend Richard Dreyfuss buys her a white dress for her birthday. She puts it on and all the other male pilots are stunned and they quickly wash their hands and line up to take turns to dance with her to "Smoke Gets in Your Eyes".
In Watchmen, Laurie Jupiter walks down the stairs to the Owl Cave in her Silk Spectre outfit, in slow motion with music and Nite Owl open-mouthed.
Narrator: Later, in the Men's Department, after discovering his long lost brothers, the jungle king was pleased to find he looked pretty good in Armani. George: Pretty darn good!
Parodied in Not Another Teen Movie. Jenny goes downstairs in her new dress and without glasses, with her family and Jake just unable to believe their eyes, then suddenly a tread breaks and she falls to the bottom of the stairs.
Jane's reaction to a fully restored Thor in Thor. Please note that she was already attracted to him before, when he was just an exceptionally well-built guy.
Jane : (grinning) This is how you normally look?
Thor: More or less.
Jane: It's a good look.
Played subtly near the end of The Journey Of Natty Gann, when Natty and Harry reach Seattle after days of hopping trains and hiking cross-country and Natty gets the chance to actually wash her face and comb her hair. Harry is visibly startled the first time he gets a good look at her after she's cleaned up.
Played with in Some Kind of Wonderful. Tomboy Watts has spent the entire movie dressed in raggedy old hand-me-down men's clothes. In the last act, when she agrees to chauffeur her best friend (and crush) Keith and his crush, Amanda, around on their date, she decides to get dressed up. The effect is striking, and she's much more attractive—but she's wearing, not a dress, but a male chauffeur's uniform. Keith doesn't seem to mind.
In the James Bond film Licence to Kill, CIA agent Pam Bouvier is insulted by the idea that she should play Bond's secretary, but when she shows up at the Bank in the dress she bought with the money Bond gave her, he's so stunned by how beautiful she looks that he does a Double Take.
Casino Royale does this with Vesper. She was previously only dressed in business suits but has to wear an evening gown for the poker game. One that James personally selected. She gets a Hello, Nurse! reaction from the rest of the players but gets this from James, having entered from the wrong door deliberately to mess with him.
Methis: I don't think I need to tell you how beautiful you look. Half the men at that table are still staring at you"
Iron Man: Pepper Potts starts off the film wearing drab business suits with her hair pulled back. But for the Stark charity gala halfway through the film, she styles her hair and wears a sexy backless dress, stunning her playboy employer, who finally starts looking at her as a romantic interest rather than just his long-suffering secretary.
Laney Boggs from the teen movieShe's All That. In this case it happens just before she's about to go to a party - overlapping with Beautiful All Along. When she goes to the prom later in the movie, it doesn't happen a second time (though she does still look nice).
A variation where it happens in Snow White: A Tale of Terror near the start of the film. Our first image of the older Lilli is her in a nightgown, so she arrives at the ball wearing her mother's dress to the surprise of many guests.
In Calamity Jane, the title character is constantly wearing unfeminine apparel and even gets mistaken for a man once or twice due to her clothing choices. Making the moment later on when she attends a ball and takes off her big, thick coat, revealing a dress and lovely figure, a shock to everyone present. And when Bill sees her with her coat off, he thinks she's someone else before it mentally clicks in two seconds later and he turns around, stunned and mouth agape. The rest of the men at the ball are pleasantly surprised along with him.
Calamity: How come all these galoots wanna dance with me? At that shindig down at Hogan's stable, none of them came around. Bill:I didn't know. Calamity: Spent most of the night chattin' with the mules. Bill: Well, it's what I've been a tellin' ya all this time... You look better in a dress.
Early on in the film, Bill accurately predicted that she'd fulfill this trope if she ever took the time to dress up.
Bill: Hey, Calam, do me a favor! Calamity: What? Bill: When you get to Chicage, notice the women, how they act and what they wear. Get yourself some female clothes and fixins'. You know, dresses, ribbons, perfume, things like that. Calamity: Look, if you don't like the way I smell- Bill: Oh, it ain't nothin' personal... Only if you ever crawled out of that deer hide and dolled up a bit, I got a hunch you'd be a passable pretty gal. Calamity: ...Well. You can save your hunches for females that get their pictures took in long underwear. I ain't one of them! Bill:(laughs loudly)
A gender-inverted example in Underworld (1927), where Rolls Royce, once he combs his hair, shaves, and puts on a nice suit, is barely even recognizable as the hobo from before.
Sabrina develops a more sophisticated fashion sense and self-confident persona after spending a few years in Paris, consequently becoming part of a Sibling Triangle with the sons of her father's boss.
See the Harry Potter example under Film, above. Except since the director of the third movie decided to prematurely tame Hermione's hair and give her more stylish muggle clothes, the sleek up-do and gorgeous dress effect on Emma was rather lost in the movie.
Hermione gets a much straighter example in the seventh book. Ron's jaw drops and he says "wow" when he sees her dressed up in a lilac dress for Bill's wedding. Hermione then jokes that his crabby Aunt Muriel said she had "bad posture and skinny ankles".
Madam Maxime is also described in very flattering terms when it comes to her choice of dress at the Yule Ball.
Gaia Moore in one of the Fearless books, although Gaia does not recognize this about herself.
Male example with Harry Dresden in The Dresden Files: Death Masks. Harry seems to enjoy the effect he has in his tuxedo when he goes to an art sales event with Susan to investigate Johnnie Marcone.
In Changes it's Murphy who cleans up nicely. Although it's a cute pants outfit rather than a serious dress, and Harry never gets to see it because the book ends with him getting shot dead before Murph can show.
Subverted in Neal Stephenson's Cryptonomicon; the modern-day female lead specifically doesn't undergo a dramatic Hollywoodesque transformation. She's as awkward in a formal dress as a tomboyish salvage diver might be expected to be, despite being quite attractive. This just serves to illustrate why he's attracted to her, though, so there's something of a similar effect.
Kit has a scene like this in the book Cue for Treason by Geoffrey Tease.
Another male example, courtesy of Louisa May Alcott. In Rose in Bloom, Rose Campbell must go to a social event and is told one of her seven cousins will go with her. She sees the guy waiting downstairs very elegantly dressed and thinks it's Charlie... but when he turns to stare at her, she's shocked when she realizes it's local bookworm Mackenzie aka Mac, thelessfashion-versed of the guys, who wears clothes borrowed from his much more fashion-oriented younger brother Steve aka The Dandy. In fact, poor Mac is so "lost" at what to do that Rose has to help him fix his cape.
Lessa in Dragonflight, who begins the book as a filth-encrusted drudge, gets this after a vigorous bath and acquires something of a bathing fetish thereafter. This trope is actually quoted by F'lar.
Though she doesn't actually do so, Herrena the Henna-Haired Harridan, in The Color Of Magic, is implied to be the sort who would clean up well. Unlike most women depicted on fantasy cover art, though, she is described as wearing sensible mail and no leather (except the boots. However, the boots are not black leather).
Redwall did this in Mariel of Redwall. Dandin is described as being surprised that the previously scruffy Mariel (then the amnesiac Storm Gullwhacker), after having been forced to take a bath and get a new green dress, could actually be pretty.
Hero Series: Lee Mallorough, at least once in every book.
In the Belgariad and its sequels, it's revealed that the regal, strikingly beautiful Polgara spent her life up to age sixteen being a filthy wreck with tangled hair, peeling skin (she doesn't tan well) and scabby knees. When her twin sister was getting married, Polgara decided to clean herself up and discovered that she was quite a looker once she'd had a bath and combed her hair straight. After the wedding Polgara went back to live with her father, Belgarath, and he complained that after being aggressively indifferent to her appearance, she went off the the other end of the scale, bathing every day, and brushed her hair to the point that on a cold day she'd build up a sizeable static charge, which would go off when she touched anything even remotely metallic.
Occurs in an Anita Blake novel to what is described as Linda Hamilton from Terminator 2 on steroids in order to distract a group of men. Anita points out that said character has the most Common Superpower so all said character has to do is do up her hair.
In the X-Wing Series, one of Corran Horn's friends tells another of his friends, and his love interest, about what he did one year at the Annual [CorSec] Awards Ball to make his date's night special. One part of this was ordering a new formal dress uniform, and it turned out that he cleaned up nicely.
Gender-flipped and inverted in Chessmen of Mars, one of the John Carter of Mars books. Gahan, the Jed (Prince) of Gathol, first shows up to court Tara in a gloriously bejeweled outfit worthy of his wealth and status. She is unimpressed. When next they meet, he is in the garb of an ordinary warrior. She doesn't recognize him and falls head over heels.
Inverted in Rats, Bats and Vats; the hero, Chip, has no interest in the heroine Virginia... until she gets nice and dirty.
The Princess Bride, where it's played straight and then again not quite so straight. Buttercup starts out as incredibly pretty anyway but moves up to Number One in the "Most Beautiful in the World" Chart when she decides to clean herself up, "unearth the territory behind her ears," and comb her hair. She does it all for Westley, though, so it's also The Power of Love.
Dairine in Wizards at War goes from jeans and a t shirt to a gown and tiara using magic, also doubles as an involuntary flashing moment.
Aragorn from The Lord of the Rings. When Frodo and company first encounter him in Bree, he is described as a gaunt-looking man, due to the long and hard years he has endured as a hunter and warrior in the wilds of Middle-Earth. When they reach Rivendell, he is noted to look much more noble and regal after cleaning himself up and wearing finer clothing. There are many points in the story (especially after receiving his family regalia in Lothlórien) where he is described as suddenly seeming taller and fairer and more obviously the heir of Númenórean royalty in the eyes of his companions.
This occurs with Aragorn earlier in his life as well, as described in the appendices: when he enters Lothlórien for the first time, Galadriel dresses him up in rich, princely clothing like an Elven-lord, so that he might catch Arwen's eye.
Inverted after the siege of Isengard. Aragorn, Legolas and Gimli are reunited with Merry and Pippin and can finally relax after weeks of chase and battle. They all sit down around a fire and Aragorn takes out a pipe for a relaxing smoke. To the surprise of the hobbits, he's no longer a lordly captain of war, but "merely" the man with whom they have travelled many miles to and from Rivendell. "Look! Strider the Ranger is back!"
Huckleberry Finn, despite the widow's noble efforts, does not clean up nicely. In his own words: 'The widder's good to me, and friendly; but I can't stand them ways. She makes me get up just at the same time every morning; she makes me wash, they comb me all to thunder; she won't let me sleep in the woodshed; I got to wear them blamed clothes that just smothers me, Tom; they don't seem to any air git through 'em, somehow; and they're so rotten nice that I can't set down, nor lay down, nor roll around anywher's.'
Alanna in Song of the Lioness gets tired of constantly looking male during her Sweet Polly Oliver routine. She gets Mistress Cooper's help in fitting a gown and "disguising" herself as a pretty noblewoman using a black wig. The first time she wore a dress, with George's mother helping her, both Jonathan and George walked in on them and both were promptly stunned by the pretty girl before them.
In Bound by Donna Jo Napoli, a Chinese Cinderella story, main character Xing Xing spends most of the story as a lowly servant. It wasn't until she properly bathed, combed her tangled hair and dressed in her mother's old clothes that she becomes the beautiful and unrecognizable "Cinderella".
In The Hunger Games, a not so small part of the preparation for the Hunger Games is all about cleaning up nicely. It appears to be more important than actually training combat skills. And while it can be assumed that the children from the first districts didn't need much "cleaning up" to be done, the people assigned to take care of Katniss nearly fainted when they saw her with her unplucked eyebrows, hairy legs, etc. Like Harry Potter above, this was lost in the film, given that "Katnip" was clearly quite attractive even before the Games.
In L. M. Montgomery's Anne of Green Gables, Anne is introduced as wearing plain, unflattering outfits, having ungracefully long legs, and having orangish-red hair which most people in the book find unappealing. After Anne grows up and is given prettier outfits to wear, there are several points where her friends and various people in the town comment on how attractive she is. In particular, when Anne is giving a monologue for an event, it's mentioned that Gilbert Blythe is admiring how nice she looks in the white dress she's wearing.
Echo Mockery in Ready, Okay! before her date with Fringie. Even her little sister and twin brother think she's incredibly hot, and Echo's date remarks that he's pleasantly surprised; he had no idea what she'd look like when she wasn't wearing a baggy sweatshirt.
Beautifully subverted in A Storm of Swords: When Gendry sees Tomboy Princess Arya in a dress for the first time, he laughs so hard that wine comes out of his nose. (He does admit that she looks nice later, though.)
Same with Brienne. She looks like a man in men's clothes. In women's clothes, she still looks like a man — she just looks like a man in a dress. Not helped by the fact that it's very hard to find a dress that fits her.
In The Rivers of Zadaa, the sixth book of D. J. MacHale's Pendragon series, Bobby is rendered drooling and speechless at the sight of Loor in a red dress, the first time she's not wearing her fur-and-leather warrior garb.
The curtains parted and a woman came toward them. Her silks and laces trailed across the polished floors. The lights gleamed on her neck and arms, and flashed from rare jewels. She was smiling brightly; and until she spoke, Freckles had not realized fully that it was his loved Bird Woman. Noticing his bewilderment, she cried: "Why, Freckles! Don't you know me in my war clothes?"
In The Fangs Of Kaath, Sandhri manages to finagle herself into the palace to find her love, Prince Raschid, and finds herself washed up and beset by tailors who manage to create a dress that best flatters her underweight figure. When Sandhri sees herself in the mirror, she is stunned and delighted to see herself transformed into the stuff of Arabian Nights sexual fantasies.
Subverted horrifically in Rebecca, wherein the protagonist dreams of this exact scene happening at the costume ball; she even orders a Pimped-Out Dress with fitting wig, has her servant check if all the guests have arrived and has the band play a sting so she can have her big Crowning Moment of Awesome. This plan fails, of course, when it turns out her husband's former wife wore this exact costume the year before; that husband then yells at her to get changed and our heroine's perfect moment is ruined.
Inverted in the Conan the Barbarian story The People of the Black Circle. Conan kidnaps the queen of Vendhya so that he can ransom her for the lives of his men. During their escape he convinces her to change into the clothes of a common woman so that she won't stand out. After she ditches her royal robes for peasant clothing, Conan remarks with approval how much more attractive she is without her fancy garments.
Conan: In those smoky, mystic robes you were aloof and cold and far off as a star! Now you are a woman of warm flesh and blood! You went behind that rock as the Devi of Vendhya; you come out as a hill-girl—though a thousand times more beautiful than any wench of the Zhaibar! You were a goddess—now you are real!
Simona Ahrnstedt has done this with all her female protagonists so far. All three of them! They're usually considered plain-looking, but once they put on a fancy dress, they will of course look really good.
Averted by Cinder in the first book of the Lunar Chronicles. She dons her stepsister's beautiful old gown to attend the ball but due to rain and her car crashing, she ends up completely soaked and oil-stained when she arrived. Not that she cares because the main reason she was going to the ball was to warn Prince Kai about Queen Levana's plan.
At the end of the first book of The Grimnoir Chronicles, Francis is rendered speechless by Faye showing up for their date in a fancy dress and makeup. She lampshades it:
"Yeah. I do clean up pretty good, huh?"
Live Action TV
Ace Lightning: Jessica Fisgus, during the dance at the end of the first season.
Angel: The titular character scores tickets for the opera. Everyone cleans up well, but Fred and Gunn, both of whom are probably the least upscale fashionable, seem to attract the most attention — especially from each other.
In the episode, "The Tale of the Closet Keepers", the resident tomboy, Kiki gets one of these. When she is revealed to the Midnight society by Betty Ann, she even gets a whistle from Gary and Tucker incredulously says, "I don't believe it! You look like... Like a girl!"
Happened again in "The Tale of the Mystical Mirror" which featured a rather homely girl starting work in a beauty shop. After a bit of primping by the owner, the girl walks out in a stylish black dress with full hair and make-up to the glee of her two co-workers. She's back to her normal clothes when she finishes work however.
She does it again two seasons later in "Atonement." This time the gown is even more revealing, and Sheridan — who is deeply and openly in love with her by that point — has an even more pronounced reaction.
Battlestar Galactica (Reimagined) (2004): The sight of Starbuck in a long slinky blue dress instead of her usual military-issue tanks or flight suit renders Apollo quite literally speechless. Lampshaded by a previous exchange between them where he teases her about her (lack of) hygiene, and she tells him she cleans up nicely sometimes. Though it should be noted, Starbuck is an Unkempt Beauty anyway, and Apollo was attracted to her long before the clean-up.
Big Bang Theory: Male example: Sheldon is known for his collection of Superhero shirts and when he has to be formal wears awful, multicolored suits. When Penny forces him to get a better a suit he looks absolutely stunning, earning a Jaw Drop from Penny and whistles from the audience.
And Played for Laughs because he refused to buy the suit because he thinks Penny made him try it on as a joke so he'd look like a clown.
The Biggest Loser: Most of the contestants for NBC's show are quite good looking once they achieve a healthy weight.
Bones: Happens (sort of) when the title character descends the stairs in an awful bridesmaid's dress. Her main love interest says she looks "nice", until Cam helps her fix the dress to be prettier. He then tells her that she looks "gorgeous" to which she simply complains "I thought you said I looked nice before!" Then in the Halloween-themed episode "The Mummy In The Maze", Booth has a similar reaction to seeing Bones in a Wonder Woman costume.
Black Books: In one episode Bernard enters the room wearing a pure white suit, looking incredibly dashing. He then furiously begins to yell at Manny, revealing that this is the real colour of his normal black suit, which Manny's mother had the nerve to wash!
Boy Meets World: Played With in one episode. Topanga suddenly becomes self-conscious about her looks, and decides to get a makeover. However, Cory and Shawn recognize that she was already beautiful before getting "cleaned up" and now with the makeover she will be "mega-beautiful", and sure enough she stuns them when she walks out of the beauty parlor. At the end of the episode she decides not to keep up the new appearance because it's not who she is.
The Brady Bunch: One episode had this as a plot point for Jan, the middle sister. She's wondering why boys — and one boy in particular — don't show any interest in her, so she has one of her brothers ask the particular boy what he thinks of her. He casually answers, "She's a good guy." Jan gets the picture, dolls herself up, and ends the episiode with a Grand Staircase Entrance before the boy in her girly clothes.
In the same episode, Buffy attempts to get Willow to do the whole "coming down the staircase" thing to impress Xander, albeit dressed as a hot goth rather than a fairytale princess. However, Willow backs out and chooses a traditional "sheet" ghost costume.
At the end of the episode when Willow in ally works up the orange to show the outfit, the dressed-up look has the desired knock-out effect - not on Xander, but on imminent love-interest, Oz who spots her from his truck (innfact Oz catching sight of Willow in unusual outfits and being intruiged by her is something of a running joke in the run-up to their actual meeting)
Played straight with Willow and Xander in the Homecoming episode. Later spoofed in a callback to that same scene when Xander is about to get married, Willow in her bridesmaid's dress looks at him in his tuxedo and comments "Good thing I realized I was gay, otherwise, you, me, formal wear... bad combination."
Subverted again in "Inca Mummy Girl" in which the gang are having a world cultures themed costume party and Willow turns up wearing an eskimo costume and Xander of course only has eyes for the Monster of the Week Ampata dressed to the nines. Willow remarks that maybe she should have worn something sexy instead but Oz is playing on stage and this following exchange happens:
Oz: Hey, that girl. Who is she?
Devon: (talking about Ampata) She's an exchange student. I think she's from South America.
Oz: No, not her. The eskimo.
The same thing happened at the end of the halloween episode when Oz was driving by and saw Willow in her hot goth costume.
Fair Cop Kate Beckett is told this explicitly using the trope name on at least two occasions: the high society fundraiser in "Home Is Where The Heart Stops" where she and Castle go undercover and the book launch of Heat Wave in "When The Bough Breaks". They're not wrong, either. The first time is a 'nervous and shy' example because she's wearing an amazingly expensive and beautiful dress that Castle has bought for her; the second time, everyone assumes she's a character actor hired to play 'Nikki', the character based on her.
Also, in "A Death in the Family", Alexis in her prom dress combines this with a She Is All Grown Up moment for her father.
Cheers: Frasier starts salivating with desire when Lilith, who normally sports a criminally tight bun, lets her hair down.
Dårfinkar & dönickar: Simone, having been masquerading as a boy at her new school, turns up to class in a dress and lipstick. Subverted in that Isak, her crush, decides he likes her back after finding out she's a girl, but before he's ever seen her in girls' clothes.
Dark Angel: Word for word. While there's the obligatory slow-mo pan up Max's dress, she's the one who says "You clean up nice" to Logan and he just says "So do you."
Degrassi: Given the age most characters are introduced at, and how long they remain in the series, most will have this moment if they aren't introduced as stylish (which is most of the cast). Usually it goes hand in hand with She's All Grown Up, male and female. Both of the Van Zandt siblings pulled this, just compare Liberty and Danny's intro looks to their last appearances, and Clare got this as a plotline.
Played straight in "The Romans" - Ian changes into Roman clothing and a slightly drunk Barbara says he looks 'splendid', even helping him style his hair correctly to fit the costume. It goes to his head a bit and he gets quite into pretending to be a Roman.
In "The Macra Terror", the usually very scruffy Second Doctor is put in a futuristic beauty-therapy machine that styles his hair into a neat parted style, pampers his skin and cleans and presses his clothes so that he looks immaculate. Polly is bowled over and calls him "gorgeous", but he expresses some reservations about the new look ("who wants to see their own face in their shoes?") and immediately dives into a 'rough and tumble machine' to put himself back to normal again, to Polly's extreme disappointment.
Inverted in "The Deadly Assassin", where when the Fourth Doctor is forced to don the elegant academic robes used by his native culture as formal dress and looks an absolute disaster, with his underwear showing and his frizzy hair poking out from under the lopsided headdress. But when the Time Lords put him in prison clothes - a crumpled poet shirt, red corduroy trousers and scratched-up knee-high boots - he looks about as dashing and romantic as he ever gets to. And even gets a bit where he gets wet.
Subverted in "The Talons of Weng-Chiang", where the Doctor makes Nubile Savage Leela dress in Victorian clothing to visit Victorian London, but the dress is really gaudy and she is massively uncomfortable in it. On the other hand, the Doctor himself ditches his usual scruffy Victoriana for very fancy and luxurious Pimped-Out Dress and looks amazing.
Subverted in "Enlightenment". Tegan changes into Gorgeous Period Dress to the amazement of everyone. Except the 5th Doctor, who doesn't seem to notice. Much to Tegan's annoyance.
Played straight in "The Unquiet Dead". Rose is ordered to change from her 21st century clothes into something a bit more appropriate for the Victorian period. The Doctor is impressed.
Martha compliments the Tenth Doctor a lot when he puts on a tuxedo in "The Lazarus Experiment", and they both compare his look to James Bond. Not that the fangirls mind his usual natty pinstripe-suit-and-canvas-sneakers getup either.
In "The Unicorn and the Wasp", Donna puts on a flapper dress for a party with Agatha Christie, and the Doctor is impressed.
Episode "Shindig": Some women at the party snark at Kaylee for wearing a store-bought dress, but she is happily vindicated when one male partygoer comes to her defense (and later the men are delighted to discover how tech-savvy she is).
It is also inverted many times with Kaylee, with Simon saying that she dirties up nicely. He says she's especially cute when she's covered with engine grease or fuel.
Friends: When Rachel heads out for her first night out with the girls since having Emma, she does this. As Ross puts it: "You clean up good!" "You clean up good" is how the trope is usually phrased in Westerns. Ross is invoking it.
Glee: Plays this straight with Quinn and Finn in the episode "Prom Queen", and Quinn does look amazing, though it's hardly a revelation since Quinn is generally said by many/most to be the prettiest girl in school.
Good Luck Charlie: Tomboy Jo, in "Duncan vs. Duncan", turns up on the doorstep in a dress for the cotillion, prompting a jaw drop and "wow" from Gabe.
H2O: Just Add Water: In one episode Zane buys tomboy Rikki a dress for her to wear at a dinner party at his house. Emma is at the dinner and her jaw drops when she sees Rikki walking down the stairs in the dress with her hair down. She's seen wearing dresses more frequently afterwards.
Hana Yori Dango: In this live action drama, Tsukushi originally comes to Shizuka's party, she's the only one not in a stylish dress. After getting pushed into a swimming pool, Shizuka dolls her up with much make-up, hair pampering and a beautiful dress. Needless to say, she finally gets everyone's attention.
Hannah Montana: Inverted in the episode, "You Are So Sue-able To Me". When Lilly's crush Matt asks her to the school dance, Miley convinces Lilly to get a Girliness Upgrade to impress him. When she later shows up at school with her new look, she has quite a few guys drooling over her, but then she gets stood up by Matt. It turns out he preferred her tomboy look.
Haven: Audrey Parker is so inept at picking out pretty clothes she has to have elderly bachelor brothers do it for her but she wears them so, so well.
How Do I Look?: This is the entire premise of this show. Take a woman whose friends don't like her fashion sense, buy her a new wardrobe, change her hair and makeup, and show her new look to a crowd of her friends and family as She Cleans Up Nicely. Often, the show gives a useful gift to the woman (besides the clothes, hair and makeup) such as paying 1/2 the past-due mortgage debt so a woman and her kids can stay in their house.
The focus of the episode "iMake Sam Girlier", both played straight and subverted. Sam is feeling down about her tomboy/ladette image and decides to get a Girliness Upgrade to impress a boy she likes named Pete. She looks quite good in her more feminine outfit, prompting an audience reaction, and even though Pete is quite smitten with her new look, he reveals that he actually liked her tough girl image better.
However, there have been other times in the series, before and after this episode, that Sam has put a dress on, and she looks quite good in them.
John Adams: Abigail Adams spends most of the first few episodes in rather plain dresses. When she does the make-up hair and nice dress thing at Versailles, her husband is lost for words. Truth in Television, adorably enough! When Gilbert Stuart mentioned that he "wished to God he could have painted Mrs. Adams when she was young; she would have made a perfect Venus," Mr. Adams expressed emphatic agreement.
Lost Girl: Kenzie in one episode when she pretends to be Hale's date for a Fae gathering.
The Magnificent Seven: Recurring character and tomboy Casey Wells is persuaded to put on a dress and fix her hair in order to impress JD. It works... for all of ten seconds, at which point she steps on her hem, tears her skirt off, and is left standing in her bloomers.
M*A*S*H: Subverted to the point of parody in the episode "Stars & Stripes". Margaret likes Sgt. (busted to Pvt.) Scully, whose attitude toward women is shall we say less than enlightened. To prove to him she's a woman along with being a Major and a Head Nurse, she gets all dolled up in an outlandish pink prom gown with Stepford pearls, high heels and lipstick. He appreciates it so much he flops down on her bed and asks her to (literally) cook him an omelet.
Princess Elena, once the Sidhe is removed from her body.
Gwen, any time she gets dressed up during the first four seasons. Special mention goes to "Queen of Hearts" where Merlin is momentarily stunned into silence when he goes to pick her up for her date with Arthur.
While Van Pelt already looks pretty sharp in her work attire, when she really dresses up to pretend to be co-worker Rigsby's girlfriend for a sting, she drives the poor man to distraction.
And Lisbon, who is often overshadowed by Van Pelt, has one of these moments at a society fundraiser that she's been ordered to go to because the CBI is broke. Jane, UST-ee/unrequited love/co-worker seems not to notice, but then he isPatrick Jane, and probably thought he could screw with her in some way by not mentioning it. Made better by the fact that when she gets called away to a crime scene, she just sticks her regular leather jacket over the top and looks eccentric and beautiful.
Happens with Fran at one point though the shock may have been due to her dress being quite garish as well as sexy. Many episodes got use out of Chateau Sheffield's sweeping staircase.
It happens for the first time in the pilot episode, with Fran coming down the staircase in a bright red, sparkly floor-length number with a slit up the side to mid-thigh.
Miss Babcock: What's that?
Mr. Sheffield:That's the nanny.
Maggie gets a moment in the same scene, with her father going slack-jawed and commenting on how much she looks like her mother.
Happens with Brighton's nerdy classmate Brooke, who Brighton (initially) didn't want to go to a dance with in "The Playwright".
Fran: -to Brighton- You see? You did a good thing and god smiled on you.
New Girl: This is Schmidt and Coach's reaction when they see Jess in the Little Black Dress her friend Cece helps her pick out... a reaction which is killed soon after, when Jess breaks into a celebratory dance.
Charlie in the episode "Sex and Drugs", when she is given a nice dress to wear instead of her usual shirt and jeans, as part of a honey trap.
At the end of the episode "Home", Tom Neville appears in a suit. He is a male example of this trope.
Robin Hood: In the BBC's show, tomboy Djaq glams up in order to infiltrate Nottingham castle. The scene features both the possible outcomes mentioned in the trope description: Will is reduced to a staring, stuttering mess and receives a somewhat sharp Moment Killer response, while Allan manages to be a little more smooth, pays her a compliment and gets the gratified smirk.
The Sarah Jane Adventures: This Doctor Who spinoff gives one of these to Luke Smith, who is rather stunned to notice that Ranidoes clean up nicely. Actually, he has one right after the other - first for his mum Sarah Jane, and then for Rani. (This version, obviously, is purely platonic on both counts.)
Sherlock: Molly Hooper puts on a gorgeous dress for the Christmas party in "A Scandal in Belgravia". John is visibly impressed, and Lestrade's jaw hits the floor.
Season 1, Tempest, Chloe dressing up to go to the Spring Formal with Clark.
Season 4, Spirit, a possessed Lois descends the stairs at the Kent Farm in one of the most hideous dresses ever seen — Clark catches sight of her and gulps. There was also perhaps a better example from season eight's Bride, where Lois comes down the same staircase in her formal wear as maid of honour at Chloe's wedding; Clark comes to meet her at the bottom in his formal wear and they both seem silently impressed.
Spaced: Parodied mercilessly in the finale. Daisy tries to make this an Invoked Trope (including a memorable sequence where she extends a lipstick accompanied by the Star Wars lightsaber sound effect) and at first appears it's working, but then it turns out that the men were actually ooh-ing and aah-ing over a spectacular flaming birthday cake behind her.
In a way, they got to this by the 3rd episode by forcing Carter into a Mongol concubine dress. No staircase, but she starts the scene with her back to the camera; after the dramatic turnaround, her teammates have few words to say.
Vala Mal Doran also does one of these in "Bounty". Of course, the only person who pays any attention to her is Cam's friend Darell.
Star Trek: Voyager: The first two episodes of the fourth season ("Scorpion, Part II" and "The Gift") presented us with the gradual transformation of the character Seven Of Nine, from a zombie-like Borg drone to the show's ultimate Ms. Fanservice.
The Suite Life of Zack and Cody: Zack is persuaded to take tomboy Max out on a date. She appears at the restaurant in a nice dress with her hair done up and Zack's jaw drops.
While the brothers Winchester are hardly chopped liver even at their slobbiest, in the episode "Red Sky at Morning" the costume designers very wisely put Dean in a tux and had him swagger down a staircase to the sounds of Bond music. A more surefire recipe for swoon-age I cannot conceive.
And then they go dropping Dean into the 1940s for an episode, with him being specifically dragged into a suitmaker because his usual jeans, flannel shirt, and jacket combo won't work in that time. Dean would look good in a paper bag, but when he steps out in a perfectly fitted suit and fedora, it's even better than the tux.
Taxi: Inverted Trope: Elaine asks Jim to go to a fancy party with her (out of concern for his feelings and with major reservations). He shows up at her door groomed and shaved, in a neato tux. Elaine gasps "You're gorgeous!" He replies in his quavering burnout voice "Yeah, I never get tired of hearing that."
The Twilight Zone: At the end of the episode "Two", the male soldier puts on an old and damaged suit... not that impressive. The female soldier puts on a white dress and puts her hair in a ponytail. He falls in love.
Ugly Betty: Mark's boyfriend Cliff has one of these at Bradford and Wilhemina's wedding, causing Amanda to quip "Who knew there were hardwood floors under that shag rug?"
One of the few things the otherwise disappointing That 80s Show (spun off from the more popular and enduring That 70s Show) managed to do well by making Chyler Leigh nearly unrecognizable in goth makeup as June Tuesday so that on the one occasion where she wasn't done up that way her natural beauty actually showed up very well.
The West Wing: Leo says this to Congressman Matt Santos...no, it's not Ho Yay, it's just meant to be taken literally.
Wings: In one early episode, Helen decides to wear a sexy dress to a cello audition. When she doesn't get the job, she isn't sure whether it was because her cello playing wasn't good enough, or she wasn't sexy in the dress. She shows Joe what she looks like in the dress, and after noting his reaction, she promptly hurries off to practice her cello some more.
Working: Parodied. Chris is one of many applicants for a newly opened position under the male chauvinist boss at the office. Chris prays on the boss's good-old-boy tendencies and general machismo to land the job. The show's main character (along with the audience) soon discovers that Chris is really a woman in disguise: Christine. When Christine outs herself, in the sauna, accompanied by all the company's execs, she returns to the office looking quite sexy in a skirt-suit. Cue one of the male characters saying "That's Chris?! He sure cleans up nice!"
In The Mighty Boosh, Howard has a subtle moment of this in the series three episode The Chokes. Normally he wears ugly, unfashionable and clashing clothes in various shades of brown, but after finding confidence as an actor thanks to a Training Montage, he walks into the Nabootique with his hair neatly combed while wearing flattering black clothing and a dapper hat. His bisexual best friend Vince, who is hinted to be in love with him, doesn't say anything, but the way he looks him up and down from head to toe with a mixture of surprise and lust on his face certainly implies he was thinking this trope.
WWE Divas such as Beth Phoenix, Tamina Snuka, and Natalya are of noticeably different body shapes than the rest of the roster and so are not really pushed forward as the "sexy" divas. However when they do clean up, the result is jaw dropping. Tamina especially considering what wonders straightened hair and figure flattering clothes can do:
REIGN suggests this as a possible justification for buying the Beauty advantage during the course of play - basically, that the character was never truly unattractive, but hadn't put any effort into maintaining their appearance and making it work. But once they do...
Subverted in, of all things, the musical Wicked where Elphaba appears at the top of the stairs at a party and everyone turns to stare, before bursting out in raucous laughter at the hideous hat she's been tricked into wearing.
In Legally BlondeThe Musical, this doesn't happen at a party, but in fact in a courthouse; Elle gives Emmett a makeover during "Take It Like a Man" so that he'll have this effect on his boss before the big murder trial, after said boss refers to him as "Tattered Corduroy." (Both Elle and Emmett have very Jaw Drop reactions to seeing his transformation - as does an entire department store staff who all call him hot.)
Played completely straight in Calamity Jane, with all attendants being shocked at seeing Jane in a dress.
A variant is done in Les Misérables. While Marius is bowled over by Cosette's beauty, he doesn't know how she used to look when she was a starved, abused child (the last time we see her in the musical). It is Eponine, raised throughout her childhood with Cosette, who gapes in amazement.
Faris from Final Fantasy V appears in a dress either once or twice in the entirety.
Battle-hardened former soldier Celes Chere from Final Fantasy VI reluctantly dresses as opera singer Maria for plot furthering purposes, causing Locke to blush red and ask "have you always been this pretty?"
Gau provides a rare male example, when he's given a makeover courtesy of the rest of the party. He ends up coming out looking like someone straight out of the Opera House (where the above example takes place, mind), and a Cloud Cuckoolander stops being crazy enough to compliment his appearance (literally the only time in the game the man manages to say something that isn't completely insane). This was roughly the plan, since said nutjob happens to be Gau's father, who went crazy after his wife died giving birth to Gau.
Inverted in Final Fantasy VIII as when we first see Rinoa she is all dolled up in her white dress at the party. Squall does take a fancy to her but they don't hit it off until she's wearing her normal clothes.
This Machinima adaptation plays it straight with all the girls getting dressed up for the Garden Festival.
Subverted in Fire Emblem where Lyn tells Eliwood in their B support that she's very uncomfortable whenever she tries to clean up nicely in the Caelin court. Understandable, since Lyn has been raised in the plains of Sacae and only arrived to Caelin during the last year.
On the Heroic Mime, much to the amusement of the player. "Am I so beautiful, that you have no words left?" We have been asking that ourselves for ages, dear princess. For ages.
In Luminous Arc 2, this happens to either Althea or Fatima, depending on who Roland was paired up with, with the dresses designed by Kaph and ends the scene with a special anime scene.
Mass Effect 2's Commander Shepard during Kasumi's DLC quest, particularly if female: she gets a Little Black Dress and heels, the only even remotely feminine attire female Shepard ever wears. However, Kasumi is the only person to comment on it, and that's just because she's the one who picked it out.
After Kasumi's loyalty mission, it's possible to select the dress as the outfit Shepherd wears on the Normandy. No one comments on it.
In the Citadel DLC of Mass Effect 3 when required to attend another event a new dress is introduced and if Commander Shepard's love interest is on the squad he/she will comment on it.
Ashley Williams' return in Mass Effect 3 came with a very stunning makeover. Of course, she was already attractive to begin with, but in the third game, many people were pleased. Otherscomplained that she was overly sexed-up.
Kumatora from MOTHER 3 had to dress up as a beautiful waitress at one point, and while we don't directly see Lucas's reaction to it (due to his Heroic Mime status), we do see Kumatora having to remind Lucas three times to "not change his expression".
Naoto Shirogane from Persona 4, if you get her Christmas Eve event.
Reivier masquerading as Duke Heath in Quintessence: The Blighted Venom had his jaw drop when Lunair enters the room in her wedding gown.
In Tales of Symphonia, depending on who the character chooses, someone will have this effect on Lloyd during a subquest. Sheena's is notably the most like this trope, though.
This also applies to Lloyd himself in a formal outfit. Sheena tells him he's handsome during the above sidequest, and Lloyd gets embarrassed.
In Red Alert 2's cinematic sequence after an Allied victory, agent Tanya is seen in a fancy dress (as opposed to the combat fatigues she wears in various cutscenes). Somewhat subverted in the "Yuri's Revenge" add-on, where Lieutenant Eva is the one invited to the fancy party, and Tanya wants to borrow Einstein's time machine to "fix things up".
a2 ~a due~: Sona, after she smooths down her hair and changes into a nice, professional outfit for a concert. The orchestra is shocked. Of course, her usual look involves piercings and a mohawk, combined with a tough-as-nails attitude, so people are understandably a little startled.
Sona: If anyone says anything about my appearance, I'm throwing them offstage during the concert.
As for Hao himself, the strict conductor with feelings for Sona, he tells her that she's always beautiful, after she nervously mentions to him that it feels weird to her too. Not before dropping all his sheet music in surprise though.
The scene in the Hidden Elf Village in RPG World is like this. Cherry all dressed up gives the Hero pause. The others think he is awed by her, but he's just impressed by the higher polygon count her character model now has.
Subverted in Cwen's Quest when the main character and resident "Action Girl" Cwen attempts to dress up to make her sister jealous only to look sublimely average. (The "Fancy Hat" didn't help any either.)
Deliberately played by Agatha in a non-canon Girl Genius short story; they didn't have stairs in the right location so she brought her own.
Then there's the crossdressing Jägermonster, Maxim.
"Max Overacts" has the "you scrub up nice" phrasing in this comic.
Skin Horse's Marcy was the physical embodiment of dowdy — until she (briefly) started dating Tip. Once that happened she took a sudden turn for the attractive, and has kept up this look even after they broke up.
One plot arc of Deer Me has Rasha and Velvet attempt to make Viana attractive by their standards, which involves removing her mask, putting her in more feminine clothing, and giving her an overall new look. She definitely becomes more attractive to Thomas, with whom she shares Unresolved Sexual Tension, but returns to her old look. Viana later confides to Woola that she doesn't like the idea of Thomas finding her appealing just when she dolls up.
Bittersweet Candy Bowl has this happen with both Tess and Daisy in the same arc, though Daisy is a more pronounced example as boys - who ordinarily ignore her - start making eyes at her. Unfortunately, the boy she actually dressed up for doesn't care.
When The Nostalgia Critic showed up in the Chick's review of The Worst Witch in an all white suit (instead of his usual rumpled one), Nella and Elisa giggled and fangirled over him, much to the Chick's irritation.
In Teen Girl Squad, it turns out The Ugly One isn't so ugly after all at her party... so much so, Strong Bad prevents the "Arrow'd Guy" from, err, Arrowing her, and proceeds to make out with the piece of loose-leaf she's drawn on. "Whoa! Did I draw that new hotness?"
In Barbie: Life in the Dreamhouse, Midge develops a crush on Ryan, but he doesn't return it due to her Deliberately Monochrome appearance, 1960s-style fashion sense, and fondness of dead slang. After Barbie and her sisters give Midge a modern-day makeover, Ryan decides to ask Midge out after all. Then he cancels the date after learning that Midge hasn't abandoned her retro hobbies.
As Told by Ginger: One episode has Ginger being forced to impersonate Courtney Grippling and so gets a makeover. When she walks into the kitchen with her hair done like Courtney and wearing stylish clothes, her mother says "wow, look at you". Although it's presented as a negative thing since Ginger starts acting more like Courtney and forgetting who she is.
An episode with a High School Dance averted this for most of the girls, though Macie did make Dodie and Chett's mouths widen when she showed up in her dress.
Avatar: The Last Airbender did it in the episode "City of Walls and Secrets", with both Katara and Toph all dolled up and Aang stunned into blushing silence and a stumbling compliment before they had even left for the party.
A more subtle example would be Zuko at the start of season three. After spending the first season being kinda ugly and the second being dirty and scruffy, the viewers finally got to see him all dressed up and prince-like.◊
Ben 10: Alien Force: A both-genders instance happened for Gwen and Kevin at the end of one episode.
Danny Phantom: Tucker gets to experience the tongue-tied moment rather than Danny when Sam dolls up for a party.
Family Guy: Parodied with Meg in the episode "Don't Make Me Over".
Generator Rex Doc Holiday dons a lovely white dress for one episode. Rex himself also looks suave in one of Six's suits and his hair combed back.
Jimmy Two-Shoes: An episode had Jimmy attending one of Lucius' formal events, on edge that he's going to find out about how he ruined things for him earlier. He states it's all he can think about...until he sees Heloise dressed up.
The Simpsons has Lisa, in one episode convinced that she's ugly, in an attempt to rectify this, Homer enters her in a beauty pageant. Lisa competes, and wins second place. Bart more or less tells her in this episode that she is quite pretty.
KaBlam!: June, the tomboyish female host is usually shown to be very beautiful in a dress, aside from her usual t-shirt, shorts, and hoodie.
It's actually stated in an episode that she'll only wear one if she's made to, otherwise, she dislikes wearing them. (Was her little act in "Won't Stick to Most Dental Work" plainly fanservice?)
Kim Possible did this one, on two separate occasions, on the stairs at her house. There's no grand staircases in High School gymnasiums, so one would think that the real-life temptation to attempt this trope for a prom date is very hard to fight for a teenage girl.
Not part of the dialogue, but clearly true for Gwen Stacy as well.
SpongeBob SquarePants makes himself over to be "long, tan and handsome" to chaperon Mr. Krabs' daughter Pearl to her prom, by way of a wig and stilts. Mr. Krabs even comments "Well he cleans up nicely" when he sees the new look.
This happens to the main trio when they prepare to go to their high school's prom in Sym-Bionic Titan. Not as much as Ilana, who usually is dressed very nicely, but Lance's hair is groomed and Octus (while trying on outfits) is able to alter his appearance to look like he's in shape.
Teenage Mutant Ninja Turtles: Occurs to April in the first cartoon, after Irma insists she dress up for a royal ball at an embassy. All four turtles go gaga over her new look and despite the fact that she's never been a slouch in the looks department, and the fact that they're...well, turtles.
In the new series Casey Jones looks damn sexy in a tux.
In the same episode, Robin himself looks quite nice in that tux.
There's another instance for Starfire, in the episode "Go!". Throughout the entire episode, Starfire has been wearing her prison garb and either screaming at everyone or being suspicious of them (since she just escaped being sold into slavery, that's understandable). At the end, when the enemy has been driven away, Starfire shows up wearing the outfit she spends most of the series wearing, smiling and looking happy and relaxed for the first time. Everyone is amazed.
Played with in episode 4 of Wakfu. When Evangelyne lets down her hair and puts on a princess gown, she thinks she must look ridiculous, but her friends are impressed. There are a few problems with this, though: they are supposed to disguise as "ugly" princesses, and Eva's cuteness makes her suspicious. Also, she can barely walks in high heels and falls several times, making the stairs part of the trope quite perilous. As for the Love Interest, Sadlygrove, he sure finds her good-looking... although he doesn't even recognize her.
Daria invokes this trope in order to convince Quinn to stop posing as an intellectual.
Done in an episode of The Weekenders where Lor develops a crush on a boy and starts acting more girly to impress him including wearing dresses and makeup and even Tino is shocked at how good she looks.
Haley from American Dad! has been shown to be pretty attractive when she wears a more flattering outfit and hairstyle.
Groj Band: When Laney participates in a beauty pageant, Kin and Kon work on her dress, hair, and makeup. She ends up looking absolutely beautiful in a black and green dress and her hair is done in two side buns. The usually Oblivious to Love Corey looks love-struck when he sees her looking like a real girl for once.
"I gotta admit. You make a cute girl...Bro!"
My Little Pony: Friendship Is Magic: The episode "Simple Ways" confirms that Applejack, the resident farmer/cowgirl, can make herself quite stunning when she wants to. Although the episode itself plays with the idea a bit, as she cleans herself up in an attempt to get rid of an unwanted suitor who's infatuated with her usual appearance.
Zig-Zagged in Clone High when first Abe, then Toots, then finally Cleo give Joan a makeover. The former two have horrible taste (Abe makes her over as a sexy nurse with a cyborg eye cribbed from a Fangoria cover) and are blind respectively, and make her look terrible. Cleo, who has excellent fashion sense, nevertheless makes her over to look like a cheap hooker, but Abe reacts as though she looked elegant and refined. Kennedy claims to like her better in her usual tomboy / Perky Goth attire, but he may have been lying to get in her pants. In the same episode, JFK makes over Gandhi in his own preppy style, which is a hit with the ladies in-universe, although to the audience he is better-looking later on in a white tux with white sneakers, although in that getup he strikes out.
Truth in Television; many people who don't like to spend much effort on their appearance every day can look amazing when the situation calls for it!
Katherine Middleton, or at least the press like to push this trope as part of her and Prince William's courtship. Apparently Wills first took a romantic interest in flatmate Kate when he saw her modelling a sheer, revealing dress at a charity fashion show.