Microsoft has created a product called "Songsmith", that creates a musical background by what you sing in the microphone. A nice idea, I suppose, but well... It starts with an extremely afwul ad (don't feel forced to watch the whole thing), and the software itself is hilarious too. People are now running the vocals of well known songs through it, which produces things like...
The Police - Roxanne
Oasis - Wonderwall
Metallica - Enter Sandman
Songsmith has a 6 hour trial download if you really want it. Entertainment in an unintended way.
Thread needs more youtube linkage! Post if something good turns up, I'm sure people are uploading new songs all the time...