All Hail Bobby McFerrin.
Valerie & I had the pleasure to see Bobby perform a few years ago at Symphony Hall. He did a solo show that was fantasic.
On his website he has two songs (Just Enough & Don’t Worry Be Happy) where you can play the role of the mixer. You can add and subract 6 tracks of Bobby singing and create your own version of the tune. Quite fun to play around with and astonishing to listen to both single and multi-tracks.

Drum Jam:
A flash interactive game where you can create your own drum-solos, record them, play them again and record new ones with the old ones playing in the background. All you have to do is move your mouse. It took me a little while to learn how to use it (read the directions).
fun stuff.