Roboto is a solid platformer for iOS that features you controlling a little robot around a series of levels, 30 in all. Gameplay is pretty strictly action/exploration based, very much in the vein of Super Mario Bros., though the robot has a few extra movies that Mario didn't have. Specifically, he can glide for a short amount of time, as well as switch gravity as certain points, which adds a little more complexity to your search for golden gears throughout the game.
Other than that, this one plays as you'd expect, and the general polish and quality makes it stand out among the many various platformers available on iOS. The one issue I had was with the on-screen thumbstick -- it's almost too close to the left edge of the iPhone's screen, so whenever I headed left, it would drop off and stop my movement, sometimes right over a gap. Other than that, though, controls are precise and intuitive, which is what you want in a platformer like this.
Roboto is available in an HD version that's universal across iPhone and iPad, complete with OpenFeint and Game Center integration, and a whole bunch of minigames and unlockable powerups and weapons. It's a solid buy, even at the current price of $3.99.