Have you ever heard the original Bob Dylan's version of "All Along The Watchtower"? I have nothing against Bob Dylan, but Jimi Hendrix did this cover wonderfully and I bet most of the people know only Jimi's version.
I don't like Limp Bizkit, their music says nothing to me. The cover was strange... bad.
My most favourite Pink Floyd cover is a powerful version of Fearless by Fish. Has anyone heard it?