I made a light theremin -- basically the same as in the Starter Kit tutorial book, but I've extended it so that it plays discrete tones (a common scale á la C, C#, D, D#, etc.).
Additionally, I wrote a simple HTML page and some JavaScript code, that changes the brightness of the computer's monitor, so that I can play music with the light theremin by "reading the song from the screen".
Check out my blog, that contains a video:
The source code is on GitHub:
Very basic, but hopefully an inspiration for someone else!