karelvanderwalt made a Phase Distortion based, music synthesizer using only a single PIC Microcontroller. Even though all digital he put a dedicated pot or switch to every parameter for an analog feel. Looks good and sounds good too, Details, schematics and more provided here.
eangolden shows how to build an inexpensive (under 100$) midi controller able to controll 2 decks. Details and more music projects can be found at eangolde's site. If you were hidding a dj inside of you now it's time to take him out. :)
Little-Scale made a simple program for SEGA Master System. The idea is to trigger drum sounds for each of the following buttons on the SEGA Master System joypad - up, down, left, right and button1. By holding down button 2 and pressing left / right / up or down, the user can select different drum sounds. The drums are synthesised by the YM2413.