wii-theremin

speaking of taking yourself too seriously...

Here's a video where the maker of a wii-mote based theremin explains how it works. He's using the infra-red sensor of the wii-mote to determine the position of two markers (one on each hand). He then maps the position of one marker to pitch, the other to volume to create a theremin type instrument.
It doesn't have to stop there - the mapping could be done so that the two markers control any parameter of the sound - giving you expressive control over any sound.