I've recently completed a LEGO drum sequencer that uses a Processing sketch to convert LEGO brick colours into MIDI notes for Ableton Live. You build music by placing 2x2 LEGO bricks on a plate. The plate is scanned using a LEGO Mindstorms NXT and four colour sensors, which then sends the colour data to the Processing sketch over USB. The sketch converts the colours to MIDI notes which is sends using SoundCipher to Ableton Live.

You can see a video of it in action here:  http://youtu.be/3bc0D2zK7YI

I've put more pictures and a copy of the code for my sketch on my website at  http://thinkbricks.net/?p=638

Feel free to contact me with comments or questions!

Thanks,

Mark