Trial Xtreme This game costs US$1.99. It's a motorcycle racing game with 60 levels that you play using the accelerometer in your phone. Excellent graphics! The physics are a little off but all in all it's a lot of fun.

Jet Car Stunts This came costs ~US$2.14 and is a 3D driving game with all sorts of impossible driving environments you maneuver through with your "half jet, half car". Controlled by the accelerometer, has 3 game modes (platform - where you just try to get to the end, time trial - where you try to get there as fast as possible, and tutorial - where you can learn tips that will help you play the other modes).

TurboFly HD This flying racing game costs US$1.99 and has 3 game modes, 8 tracks, and 5 ships with weapons and boosts (making it more than just a racing game). beautiful graphics - you can use the accelerometer or the touchscreen to control. The only downside is that it could use more levels!

Need for Speed Shift2 This is an AWESOME car racing game that lets you drive 20 luxury/racing cars across 18 tracks. You can customize and upgrade the cars. There are a few different game modes, and has beautiful graphics. It works on my phone but I've heard others with various phones complain of compatibility issues.

Raging Thunder 2 Beautiful car racing game that costs US$4.99. Intuitive controls, multiplayer racing, and tons of levels. Recommend!