MotoHeroz. Originally debuting on WiiWare, this game is – well, it's basically Trials. If you haven't heard of Trials, then you really need to start reading our site more.
In short, MotoHeroz is a physics-based side-scrolling racer with platforming elements and a really depressing leaderboard where your friends show you how much better they are at the game. MotoHeroz is free to download on all iOS devices running version 4.1 or greater.