Everyone must have played racing game on mobile phone. PadRcaer (racing game for ipad) allows you to use iphone or itouch as steering wheel.
PadRacer is an old school, top-view racing game that can link up with not one, not two, but four iPhones (or iPod touches) as controllers.
Best of all, the iPhone controller app is free, so you only need to buy one version of the game on the iPad and three of your buddies can bundle in on the fun for free.
Reminiscent of the likes of Super Cars on the Amiga, the gameplay is simple (steer your car around the track, try not to crash, try to win), which leaves you to concentrate on the fun of using your iPhone as a steering wheel.
there are other games like scrabble and chopper 2.
read more about it on ipad-games-iphone-controller