Microsoft recently released Songsmith, a “product” that allows you to sing to a beat and then it creates backing music based on your vocals. I think you can pick the style as well. Anyway, it’s scary.
There are tons of videos made by people taking a capella tracks of popular songs and running them through the program. Just search for Songsmith and become horrified.
That said, here is a pretty hilarious Metallica/early Depeche Mode hybrid for “Enter Sandman”
Just for good (read: bad) measure, here are two versions of “Hot For Teacher”