On a lark I bought the most recent issue of Make magazine. This issue was all about the Arduino, an open source prototyping microcontroller. So I ordered one, and so far I am having a ton of fun. I even started a git repo to store my "sketches" (which are the C code which program the microcontroller). So far the best I've done is make a music box on which I can control the pitch and the tempo with two different types of potentiometers. The sky is the limit, and I keep coming up with new ideas to try.