Most rousing demo award at TechCrunch50 goes to Bojam, simply because they had the music ("Africa," by Toto). The service is a music mixing product and online store.
Artists can lay down new sounds on top of tracks other people have recorded previously, and anyone with access to the tracks can mix music.
New completed songs can then be sold on the site.
The demo was loud and entertaining, and the technology is cool. If you're a musician looking for a jamming product, also check out eJamming, which I covered from the at the January 2007 Demo conference.