Toysight. Use your iSight camera to play games, sort of like the Sony EyeToy, but Apple-sauced.

‘Toysight is set of cool games and toys to play using your iSight� or similar firewire camera.
Using a system of object and motion detection to track your position, Toysight allows you to control buttons, sliders and perform gestures on the screen, putting you right in the action!’