One game that jumped out at me while I was pawing through the virtual game racks at the App Store was Crash Bandicoot Nitro Kart 3D from Vivendi Games Mobile.
A racing game featuring Playstation perennial Crash Bandicoot, Nitro Kart 3D is sure to wear out your iPhone batteries quickly. This app uses the accelerometers in the iPhone for control; turn the iPhone left or right like a steering wheel to turn, and tilt the phone up or down to accelerate or brake.
The entire time you're racing against the other characters, including the nefarious Brio, you need to avoid oil slicks and weapons used by your opponents, try to pick up a little time by hitting rainbow-colored "hyperdrive spots" on the track, and hit boxes containing weapons (like surface-to-surface missiles, my personal favorite) so you can slow down the other racers.
The game is localized for English, French, Italian, German, and Spanish, and you can adjust the sensitivity of the accelerometer to keep you from over-controlling your kart. With smooth 3D graphics, fun sound effects, and the enjoyment of waving your iPhone around to steer, Nitro Kart is well worth the $9.99 price in the App Store.