Ray Alder of Fates Warning did a side band called "Engine" and they recorded a hard rock version of The Cure's "Fascination Street". Peter Parada (whom I went to school with and is now with The Offsping) played drums:
Dream Theater did a great version of Elton John's "Funeral for a Friend" back in the 90's that was excellent:
but gosh, there are so many, I could be here all day:
Dream Theater's version of Ozzy's "Diary of a Madman"
Type O Negative's version of Neil Young's "Cinnamon Girl"
Judas Priest's version of the Joan Baez song "Diamonds and Rust".
But here is an odd one:
Rasputina did a version of Led Zepplin's "Rock and Roll" on just two cellos, voice and drums. It's really weird, and almost wrong, which is probably why they did it.
Here is a badly recorded live version: