Here’s a quick video of a current project of mine, the CarrerPIa GT. It’s a remote controlled car with a Raspberry Pi inside to control the motor and steering; the car is controlled from an Android phone, with a webcam feed from the car.
The car is controlled using the PiFace breakout board and a bit of basic circuitry, and the hardware side of a project like this is fairly basic. For more info on how the car works, see the video! I’ve put the source code for the car and the phone on my Launchpad profile.