Zappa's cover of "Tied to the Whipping Post" is awesome. It's on a video, "Does Humo(u)r Belong in Music?"
And an odd one: Loreena McKennitt doing what she describes as a Tom Waits version of Greensleeves.....
And Ten Years After, with Alvin Lee, de-Bowdlerising "Good Morning Little Schoolgirl"
Martin Simpson's "Masters of War"
What does get up my nose is when I hear a covers band say something like "We'd like to do a Guns'n'Roses track...." when it's by Dylan.