A quick and easy way to start making interesting MIDI signals is to use a joystick or joystick-compatible device mapped to MIDI with my joy2midi utility. I've tried it with a gaming joystick, but there are more exotic options like 3D mice, which act like 6-axis joysticks. All the controllers for the RockBand game are actually just joysticks with interesting shapes. There are probably many more out there if you look.
The tonestrip is the first piece of electronic hardware I've built in a long time. Man, things have come a long way since I last burned my fingers on a soldering iron! For one thing I finally discovered the joys of wire wrap (just when it's going out of fashion again, apparently) so I'll never burn my fingers that way again. But the power, ease of use and flexibility of ARM microcontrollers these days blows me away. I'd been hearing all the Arduino buzz but hadn't realized how far we've come from those 8-bit PICs I burned up back in high school. And yeah I'm sure Arduinos are cool, but the Teensy is even cooler because it can register as a class-compliant USB MIDI device, making it super easy to achieve plug-and-play MIDI input.