Did you know that the Wii remote contains a 1024x768 pixel infrared camera? With this knowledge an a bunch of IR-emitting LEDs and tape, Johnny Chung Lee, a student at Carnegie Mellon, has done some truly amazing things. Multi-touch screen, Minority Report-like interaction, 3D scenes controlled with you heads movements, etc.
Oh, and of course Mac addicts should try Darwiin-remote to use the Wiimote as the Mac's mouse (or whatever you want). What, you didn't not know that the Wiimote is also a Bluetooth device?
If you don't have a Wii, the remotes are sold separately and are quite cheap. Kudos to Nintendo for having invented such an amazing device!