My friend Tim and I built a piezoelectric drum machine based on the PIC32 and an Altera Cyclone III FPGA. The video below demos a kick drum and a snare drum - both drums are capable of playing at the same time, and the hit strength determines output volume.
I've included a writeup for the project, which contains circuit schematics and all necessary code with the exception of the actual sound files. If I could redo the project, I'd get rid of the LED's in the circuit and replace them with zener diodes to help with voltage regulation, but on the whole I'm happy with how everything turned out. Well, everything except the all-nighter just before the due date.