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.).
Check out my blog, that contains a video: http://danbod.blogspot.se/2013/03/arduino-project-screens-brightness.html
The source code is on GitHub:https://github.com/bodnerdan/js-arduino-theremin
Very basic, but hopefully an inspiration for someone else!