There are low-cut outfits... and then there is Absolute Cleavage. This is when a dress or top is specifically cut to show the entirety of the wearer's cleavage and the top half of her stomach...or the bottom half, if they really want to court tabloid immortality.
A Spy Catsuit is frequently one zipper away from this trope. Very slightly justified in that, if you're dumb enough to wear a tight-fitting catsuit on a spy mission, unzipping the front will give you a lot more mobility in the arms and shoulders.
There may be a bra underneathnote There are special bras that create absolute cleavage without getting in the way. The technical term is "plunge bra", but generally there isn't. In any kind of real-world or live-action context, generally requires some form of adhesive to avoid a Wardrobe Malfunction.
Compare Sideboob, Underboobs, Impossibly-Low Neckline, Cleavage Window. Its Spear Counterpart can usually be found on the Walking Shirtless Scene, complete with MANLYchest hair. Any woman who ends up in an outfit like this is probably Ms. Fanservice.
Cecile of Code Geass dresses up rather provocatively in one episode during a formal meeting. In the next episode, Milly dresses up like this during the pre-wedding ceremony between Prince Odysseus and Tianzi.
Early InuYasha villain Yura of The Hair makes use of this trope.
Angel and Ultear of Fairy Tail like this. It's more notable with Ultear because up until she donned it she'd been wearing a gorgeous, tame kimono.
Inori Yuzuriha from Guilty Crown has a few outfits that provide this. Most notably: the skintight, red outfit she wears in the beginning, the black outfit of feathers in her Egoist music video in Episode 1, and the skintight white suit.
Pretty much all of the female characters in Rio -Rainbow Gate!- are guilty of wearing skimpy outfits. However, it is the main villain, Cartia, that walks around with not only the biggest breasts, but a dress that showcases most of her cleavage.
In Beelzebub, Yolda the demon manages this with a corset, as one of the things that distinguishes her from Hilda. Which Hilda uses to her advantage when she pretends to be Yolda.
The Golden Age — later revived by Eclipse Comics — series Airboy included former villainess Valkyrie.
Lampshaded in The Boys. After discovering that Justice League of America analogues the Seven are super-pricks, their newest member Starlight is told that their corporate sponsors are redesigning her much-less-revealing outfit into this while the Superman analogue the Homelander draws the new neckline on her current costume with a Sharpie. While she's wearing it.
Doubly creepy because the Homelander, among others, had recruited her via the Casting Couch.
When Emma Frost first joined the X-Men, her costume was an unholy mix of Absolute Cleavage and Impossibly-Low Neckline, due to being a few strategically-placed scraps of clothing that formed a reverse "X" with her exposed skin.
Death Becomes Her: That one gown Lisle wears, the one held together by one sole button in front of her crotch. And this is just about the largest and least revealing piece of clothing she is seen in throughout the movie.
YT from Snow Crash wears a zipper-front jumpsuit, and unzips it further than modesty would have suggested to discomfit a (slightly) Dirty Cop who's not sure if he's up for some Prison Rape or not.
YT: Make up your fucking mind.
Conan the Barbarian: The attire of Bêlit, the she-pirate in one of the most classic tales by Robert E. Howard, Queen of the Black Coast, is described as being only a "broad silken girdle", i.e. she is a rare case of a female Walking Shirtless Scene. This was obviously not carried over to the comics adaptations by Roy Thomas and John Buscema for Marvel comics, where she wears something similar to the description of this trope. Whereas in the Finnish comic adaptation by Petri Hiltunen, her attire is faithful to Howard's text.
During Rogue Squadron's insertion into Coruscant in Wedge's Gamble, Erisi Dlarit wears a rather loose outfit featuring this, only gathered at the waist by a belt. In the words of the narrator, anyone with the brain of a Kowakian monkey-lizard could figure out what she looked like naked.
Commandant Mele-on-Grayza in Farscape There was a reason Crichton nicknamed her "Commandant Cleavage" after all.
When called out on it by Akhna (the female Scarran War Minister), Grayza replied "Would you have a weapon in your armory and leave it unused out of squeamish good taste?"
Elvira: "If they ever ask about me, tell them I was more than just a great set of boobs. I was also an incredible pair of legs!"
Elvira: "It's me again, yours truly, Elvira, the gal with the enormous...uh...ratings"
Unsurprisingly, Manswers once asked how skimpily a woman can dress before she's legally naked. The absolute limit consisted of two vertical ribbons in front and one slender thong in back; the ribbons' elongated-vee arrangement constituted this trope.
Specifically, the garmet (such that it exists) must completely cover the nipple and areola, as well as completely cover the vagina and anus, plus pubic hair. Less/no hair, technically less fabic needed.
Sherlock: Irene Adler wears a see-through green kaftan like this...for about two seconds, whilst looking for another outfit.
Margaery Tyrell in Game of Thrones on her first appearance in Renly's encampment wears a dress which leaves very little of her cleavage to the imagination. This being Game of Thrones, of course, it doesn't take long for the imagination to become unnecessary.
Quite a few female musicians favor this outfit. Kylie Minogue is a clear example with her massive cleavage in the "Can't Get You out of My Head" video. Other examples include Britney Spears' Elvis suit and Lindsay Lohan's loose dress.
P!nk has one in the start of the video for "Just Like a Pill".
Lady Gaga wears these a few times, and in the case of her "Telephone" video, it's questionable if they even count as shirts.
Trina in the music video for "Pull Over".
Moran Mazor, Israel's entry in the 2013 Eurovision dsipalyed her assets in such a dress.
The dress worn by the "beauty" in the "Beauty and the Beast"-inspired video for Meat Loaf's "I'd Do Anything For Love (But I Won't Do That)" is a full-length dress which is gaped open in the front and just barely held in place with lacing, to give it this effect.
The blonde girl's blouse has all but two buttons unbuttoned with the blouse being tied at the waist in the video for "Caught Up In You" by 38 Special.
Lita, after she hooked up with Edge, started wearing this sort of tops. Even her "wedding dress" was made this way.
Elisabeth: Frau Wolf, the brothel madam, in the Essen and Stuttgart productions wears the lacy-bra variant with an otherwise Victorian dress.
Metal Gear Solid: Sniper Wolf was dressed this way. (Lampshaded and Justified in The Last Days of Foxhound. It turns out that her then reasonable jumpsuit shrunk in the wash (which may or may not have been done on purpose by Decoy Octopus). She was pissed because they were at Shadow Moses and she was freezing with it on. Later, there was The Boss during the final battle in Metal Gear Solid 3 and EVA during almost the entire game. Though in the case of The Boss, her open suit was meant to show off the scar running down her front. Also, Naomi and Big Mama in Metal Gear Solid 4 (though since Big Mama was EVA, to the surprise of some, this somewhat makes sense).
Dragon Age: Origins: Morrigan's outfit, consisting of an oddly patched-together skirt and a mage's hood that looks more like she draped a scarf over her shoulders. Adding to this, her entire back is exposed and seemingly only a few strings are keeping the thing together.
Rayne in Blood Rayne 2. A little more cleavage and the rating would have gone up.
In the Japanese PS3 version, Judith also has an alternate outfit that is an evening dress with this. The difference being that she knows the effect she has.
The fan-made Neverwinter Nights module "Aribeth's Redemption" includes an item (female characters only, not that you are allowed to play one) entitled the "Armor of Impossible Cleavage." It consists of an ordinary suit of gold chainmail with a foot-wide strip of nothing down the entire torso. The person who wears it is a priestess of the setting's goddess of physical beauty and sex.
Linda Vermillion from Killer7 had an outfit like this.
Silvia Christel from No More Heroes. Appropriate, as she's named after a porn star.
Every Female Character gets one of these in Mortal Kombat 9. It gets a little ridiculous how their vast tracks of land can stay in those costumes when there is more cloth in their mask than their tops.
In Fable II, if you're playing a female hero and put on the Bandit Shirt, you get this.
In Mass Effect 2, the Justicar Samara's "combat armor" features this.
Mai Hem in Perfect Dark Zero has this in mission 4, with a wraparound top that shouldn't be able to stay on.
In Neptunia, Nisa dresses like this despite being flat-chested.
HDD Uni and HDD Vert have this as well. In Vert's case, it's slightly more egregious for her in Neptunia Victory.
In Catherine, the host of the Golden Playhouse, Midnight Venus, wears an extremely low-cut suit jacket with nothing underneath.
Darkstalkers character Morrigan's iconic outfit technically "only" possesses an Impossibly-Low Neckline and a cut-out right below said neckline that, combined, reveal her entire cleavage and the top part of her stomach.
Two Worlds has this in the case of Kira. The odd part about this is that Kira is the male protagonist's sister, making her an odd choice for the obligatory Fanservice girl.
Fear Effect. Hana's green party gown in Fear Effect 2. As Rain said, "You're wearing that?! Why don't you just walk in there naked."
Azura's statue in The Elder Scrolls V: Skyrim has this. Which is a bit odd, considering the two previousgames followed her appearance in Daggerfall and had her statues show her topless, and her actual appearances in Morrowind had her dressed more modestly. Nocturnal wears a robe that shows off her cleavage, split down to her waist.
Lost Odyssey's Ming has a leather corset-thing under a cropped top that features a wide expanse of her cleavage almost down to her navel. How her cleavage doesn't pop right out is a mystery. We even get a cutscene that could be an excuse for a closer look.
Erfworld: Resident Ms. Fanservice Wanda once showed up wearing this. She's wearing the outfit from Thriller, and didn't zip it up all the way. Later, her evil sorceress outfit qualified too.
In The Order of the Stick, Haley being persuaded to sport an Absolute Cleavage was taken as proof by Sabine that Nale intended to sacrifice her.
Monette in Something Positive once wore an Absolute Cleavage shirt in support of the Boobquake campaign.
In The KAMics when Gertrude & Brunhilda got some "space suits", Gertrude's outfit demonstrated this trope.
Enforced when Tanna — normally a tomboy learning to track and shoot and disgusted by girly stuff — of Ears for Elves is played for fanservice by wearing high elf clothing in the first Q&A page. She is not exactly impressednote To quote, "What the shit is this?!!" with her new outfit. This version of her (nicknamed the "Anti-Tanna" by the artist) has a small reprise during the announcement for the second Q&A series.
In the King of the Hill episode "Hanky Panky," Debbie Grund is seen wearing an extremely low-cut dress (and death-defying boobs) to the formal dinner at which Hank accepts his Blue Flame of Valor Award.