Okay, I was listening to Adam Curry's podcast, The Daily Source Code, and he played a song from an 'album' I'd only heard about. It's called Beatallica, and is a mashup of Beatles songs sung as if written and performed by Metallica. The example he played was Hey Dude, and it's ... just ... wrong.
Others I don't intend to try, but am amused by the titles:
Got to Get You Trapped Under Ice
I Want to Choke Your Band
The Thing That Should Not Let It Be
Just visit the link and try to match up the originals with the mashups.