Lots of good ones. The Johnny Cash version of NIN "Hurt" is one of my favorites.
Bruce Springsteen is a huge entertainer, but two of his songs, I felt were done even better as covers:
Because the Night:
Spirits In the Night:
A couple of Iggy Pop covers:
A few great Simon and Garfunkel tunes covered:
Some more cool covers...
This was a great re-mix:
Of course, some covers makes you just go...
ADG