I first saw this stuff years ago and had completely forgotten about it - thanks for the reminder! Here's their site:

http://www.animusic.com/

Some are cooler than others but they're all worth watching. Here's an interview with the creators:

http://www.youtube.com/watch?v=ZYrYqA8lO0U http://www.youtube.com/watch?v=2TzvuPB8ttU