If you're looking for something comfortable, sexy, aerodynamic, sexy, smooth, and sexy for your characters to fight in, party in, or just walk around in, there's no reason to look no further than skintight pants, preferably spandex or leather so that they can be shiny too.
Unless they're spandex, the "fight in" thing doesn't really work. Seriously. Female characters with nice legs and buttocks almost always feature a fanservice-heavyfighting style with lots of high kicks. Ask your local tae kwon-do coach to teach you some high kicks. Now put on some skin-tight leather or denim pants. Now do your high kicks. See the problem? That problem arises only if we're assuming our super woman hasn't broken an ankle running about in stiletto heels or thrown herself to the ground from her own jiggle momentum, of course.
These are gold mines for having fanservice without looking too blatant and seeming hip at the same time: they're tight and shiny, which means that they show off every curve and contour of the wearer's body, and, in games, allow for heavyJiggle Physics. Extra points if the wearer is wearing a top out of the same material, covering all the fanservice bases.
These really became popular in the Seventies and Eighties, and are used much, much more often on females than males. See also Most Common Superpower, as clothes like this are used to emphasize that.
See also Superheroes Wear Tights.
Note: Full skintight bodysuits are a different trope altogether, as are cases when the outfit really is painted on. Form-Fitting Wardrobe is for when clothing clings like this but is made of materials that shouldn't.
Examples:
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Anime and Manga
In Mahou Sensei Negima!, Chachamaru occasionally wears stuff like this. Not to mention that she has thigh high stockings literally built into her synthetic skin.
Neon Genesis Evangelion justifies this by having the costumes start out loose and baggy, but conform to the body with a vacuum-seal.
Nausicaä of the Valley of the Wind has the titular princess in form fitting white leggings however as Miyazaki is a feminist they aren't really played for fanservice. However the film did once have a reputation for having viewers think that Nausicaa was flying around pantsless and underwear free due to old VHS fansubs where the footage had degraded so much through multiple copying that they looked more skintoned in colour.
Comic Books
Marvel is all over this; Basically, any Marvel superheroine who isn't wearing a full bodysuit has this, and every other female character after that.
Nearly every X-Woman has had an outfit like this at one time or another. Storm has this when she's not using her other outfit, several characters have this as their main outfits, such as Jubilee, Emma Frost, and Marrow.
Male comic characters also frequently appear to have been drawn naked but with Barbie Doll Anatomy, and then colored like a Captain America suit, to the point of details like belly buttons showing. Really, clothes hanging like actual clothes is the exception, not the rule.
Used quite obviously in X-Men Legends, where every single female character wears something like this or tight jeans which have the same effect.
Poor Empowered's super suit is canonically thinner than a soap bubble and so revealing it took her six months to work up enough nerve to wear it in public.
Eddie Murphy used to wear clothes like this in his stand-ups in The Eighties. To paraphrase Scrubs: "No wonder he called it 'Raw'".
The page image is Amy Adams as Amelia Earhart in Night at the Museum 2: Battle of the Smithsonian. (Adams on donning the pants: "Hey, I do have an ass!" Men everywhere: "Hell to the yes.")
"Sandy II" in Grease. Olivia Newton-John had to have the pants sewn around her legs, so tight were they.
Superskin, a bodystocking that fits like a second skin in Robert A Heinlein's Friday.
Live Action TV
Eric Estrada of CHIPs admitted the costumers sewed in extra zippers on his pants at strategic places.
Half the cast in Blake's 7, Avon in particular. The infamous "lobster suit" apparently gave Paul Darrow some trouble when it came to running.
Jenny, the Doctor's daughter in the new Doctor Who.
River Song is also fond of pants very similar to the ones in page picture, even managing to run and fight in them.
Amy Pond generally opts for these when she's not in the mood for her usual mini skirts.
Kurt Hummel from Glee. His pants are sometimes so ridiculously tight you have to wonder how he can even walk in them at times. And he does do high kicks in them. Check out both 'Rose's Turn' and 'Time Warp' for proof.
In another male example, Dr. Spencer Reid of Criminal Minds sometimes wears pants that show off his long legs and assets.
Robert Conrad in The Wild Wild West - his legwear of choice is so tight that in fight scenes they were prone to splitting (and not always off-camera, as "The Night of the Pistoleros" demonstrates).
Dolly Parton's "Why'd You Come In Here Lookin' Like That":
Why'd you come in here lookin' like that, in your cowboy boots and your painted-on jeans?
Steve Perry of Journey wears these in the "Just The Same Way" music video.
Theater
Mimi's famous blue "Out Tonight" pants in Rent. Note that the actress wears them while dancing on a railing.
Forbidden Broadway's Rent parody included a song called "Ouch, They're Tight!"
In The Rose Tattoo, Serafina examines her daughter's sailor boyfriend from the front and back and asks him why they make Navy pants so tight. "That's a question you'll have to ask the Navy," he tells her.
Professional Wrestling
Popular in Professional Wrestling, for both male and female wrestlers. This occasionally comes up for characters who are homages to wrestlers as well (such as Hugo from Street Fighter).
Video Games
This was often used in earlier 3D games due to technical limitations. You don't need to render creases and ruffles for something that literally looks painted on.
In Soul Calibur III and IV, given the setting, no character wears this except, arguably, Xiangua, but in the character creator (where they have everything from eighties clothes to skintight chainmail) you can set female characters to wear these. In Soul Calibur 4, with it's constant Clothing Damage, it usually comes down to either these or underwear/bikinis.
Taki's entire outfit seems painted on. She's basically modelled as though she were naked but coloured red.
Sonya Blade alternated between this and less tight pants, though she stopped wearing these in the later games.
City of Heroes, saying as how it's of the superhero genre, has a multitude of shiny tight pants options, from spandex to leather to metal.
Champions Online meanwhile seems to have few options other than that.
World of Warcraft uses these for most equipment, using different pieces attached to the base model to make it unique. It gets a bit ridiculous for some equipment, for instance skin tight plate mail or skin tight tuxedos.
Final Fantasy XI uses this for some equipment, notably Elvaan starter gear, both male and female.
Miranda Lawson from Mass Effect 2 certainly lives up to this trope. Her second outfit that you can unlock by completing her loyalty mission makes her look as if she dips herself in a bath of liquid black latex every morning.
Old Snake from Metal Gear Solid 4, Justified, as loose clothing would hamper his sneaking ability, and it's a muscle suit about an inch thick, to make up for his old age.
Fenris of Dragon Age II has very, very tight pants. One wonders what they're made of, given that his low-tech world is unlikely to have spandex; his outfit is given no more in-game description than the mystifying "Grafted Spirit Hide." (How does a spirit have hide?) Rule of Sexy probably applies.
In fashion fetishism, they have the concept of a second skin, where a fabric usurps the sexual role played by bare skin.
"Skinny jeans" are all the rage, and for good reason—when it comes to attracting the desired gaze, they work. Leggings are even more so. Now there's even faux denim leggings ("jeggings"), complete with false pockets.
English riding breeches. On purpose.
Running tights. For that matter a lot of athletic clothes are skin tight. It reduces chafing, helps wick sweat away, and if you're an athlete, shows off that body you've been working so hard on.
Cycling shorts are so tight, racing designs tend to shy away from white because they can be a little too revealing.
Swimsuits for professional swimmers are getting nearer and nearer to this trope...so much so that the international swimming federation is starting to crack down on suits that are too painted on...(this is justified however, in that the less loose fabric, the less water resistance)
A properly-fitting wetsuit tends to be like this. And you think tight jeans are hard to take on and off, try ones made of what basically amounts to a body-shaped non-slip mat.
Spandex in bike tights, et cetera. Spandex hadn't been invented when they first drew Superman, and George Reeves' costume in The Adventures of Superman is almost baggy by comparison with Spandex.
