This was one of the first iPhone games I blogged about and after a year I'm still playing it. Moto X Mayhem is a fun iPhone app where you ride a dirtbike over different terrain, take jumps, go through tunnels and try to reach the end.
Here is an example of completing a jump!
As well as some great graphics, there are some funny sound effects when the biker does a wipe out! You can actually hear him/her grunt! Using Autorotation (rotation transformation) on your iPhone, you can control the pitch of the bike and even complete a loop if you go off a jump.
It's very entertaining!