http://www.cs.cmu.edu/~johnny/Not sure if this has been posted here, but this is cool.
Check out the WiiMote tricks section. By connecting a wiimote to your PC via bluetooth and building a small infrared LED pen, you can turn your screen into a multitouch display.
ah my alma mater, what a geek wonderland
That bloke is prolific! Great stuff - and he even invented a $14 steadycam which might come in handy for me...
After looking at this guy's stuff I had a neat idea of my own that could be implemented in Blitz if one we so inclined.
The idea is this:
Use a webcam to do motion tracking and determine where a user's head is relative to the screen. Then use that position to adjust the angle from which a camera is viewing a 3D object that is displayed on the screen.
Wouldn't provide different viewpoints for each eye, but you might not need to to make it somewhat convincing. You can get a 3D-like effect by switching between two images fast, or with parralax. So if you could track someone's head accurately enough, maybe the small movements they make naturally would move the camera enough to allow this parralax 3D effect to work.
One might be able to improve this further with gaze tracking. Ie, determining where the person's pupils are, and using that to tell if they're looking at the center of the screen, or the sides.