First, the more 'boring' one. BBC reports on auditory interfaces, and using objects to emit sound with function. Cool? Sure. But, I'm not sure what it would be used for.
Second, and totally awesome, an independent programmer has turned the Nintendo Wii remote into a head tracking device. The result is absolutely incredible in both its simplicity and resulting quality. Watch the video. You can skip to 2:05 if you don't want the background info. Stuff like this makes me giddy about the innovative uses for simple technology.