Arduino

Using an arduino as a MIDI Output Device:

http://itp.nyu.edu/physcomp/Labs/MIDIOutput

http://createdigitalmusic.com/2006/10/diy-midi-drum-triggers-with-arduino-midi-over-usb/

http://www.arduino.cc/

http://www.liquidware.com/shop/show/AMEGA2560/Arduino+Mega+2560