Endless runners a la Temple Run are fast becoming the default genre for mobile games, and with good reason. Their one-touch play style is perfect for touchscreens, and the short levels work well for bite-sized sessions. That said, it's always nice to see a little innovation, and iOS pilgrim Roller Rally has that in spades. In addition to a competitive racer format, it's got great graphics and tight controls.
If you've ever played the console snowboarding game SSX, you'll be on familiar turf here.