I know this is one app in a billion, but I kind of got hooked onto this last year. It's called "Bounce On", and it usually goes to 2-4 dollars. But in spirit of the holidays, it's free. It's like a mix of Sonic and Mario, and the graphics are very cute. Team Phobic, the creators, have made 5 worlds, many of the levels are quite difficult. It's a tilt and touch app. If you're a Mario or Sonic fan, you may want to check this app out before it loses it's status of being free.