Single-Power Superheroes

There are many superheroes out there. Some, like Batman, do their super-heroing using years and years of training their bodies, showing human capability to a remarkable extent, possibly with the help from a utility belt as well. Others are like Superman, having a whole grab-bag of superpowers that needn't even be remotely related in some of the extreme cases. Then, there are superheroes like The Flash. Beast Boy. Static. The middle-roaders. The ones that only have one listed superpower, but which they sometimes have many uses for.

As you can guess, this trope excuses unmentioned Required Secondary Powers, since they often aren't a power in their own right, though the line can get a little fuzzy at times. Elemental Powers are a sub-trope of this. In a show with Cast Speciation, this can easily become What Kind of Lame Power Is Heart, Anyway?. (See Hawkman in the Superfriends cartoon.)

Anime and Manga

 * Contractors in Darker than Black have only a single power. They might be creative with it, but it always comes back to one general ability.
 * The espers in A Certain Magical Index and A Certain Scientific Railgun generally operate like this. They have one very specific power that they can use in all sorts of ways (for example, Misaka can stick to walls, shoot lightning, create railguns, hack computers, and so on... but it's all electromagnetic control). They even mention "Dual Skill" being a myth in one first-season episode of A Certain Scientific Railgun. Mages tends to be a bit more complicated.
 * Devil Fruit from One Piece gives a person one super human ability. What regular humans can do in that universe would be super powers pretty much anywhere else though.

Comic Books

 * A significant number of characters from X-Men. Cyclops, Quicksilver, Magneto, Polaris, Dust, the Stepford Cuckoos, Rogue (even though she uses her one power to get many), Mystique, Gambit, Shadowcat, Professor X, and almost too many others to mention.
 * From DC Comics, we have Flash, Hawkman and Hawkgirl, Wildcat, both Wonder Twins, Metamorpho...

Film

 * All superpowered characters in Sky High are like this, outside of Will who inherited one power from each of his parents.

Live-Action TV

 * Most superpowered characters in Heroes have only one power, and many others have "related" powers (eg Hiro Nakamura can bend time and space).

Tabletop Games

 * Due to the way the Hero System rules work, on paper most of the characters from the Global Guardians PBEM Universe have multiple superpowers on paper. Functionally, however, what most of them have is just a single power for which they've discovered multiple uses. For example, Bungie is a Rubber Man who has superior strength (because she can use her strechability to change her point of leverage in her own body) and invulnerability to most physical attacks (because her elastic body stretches with the force of the attack), and can change her shape (by stretching her body into various forms), but it all boils down to Bungie stretching.

Video Games

 * Almost every character in Gensokyo has one special ability. Granted, almost all of them choose not to use them, but having game breaking abilities like the ability to invoke death and the ability to destroy everything available for use is a bit of an unfair advantage in hindsight.

Western Animation

 * All benders in Avatar: The Last Airbender have control over only one of the four elements. The Avatar is special not just because they're significantly more powerful, but that they are able to master all four elements.