Okay, totally seconding (thirding?) the Jeff Buckley and Placebo.

Some of my favorites.

Sarah Slean - Climbing Up The Walls (Pink Floyd cover)

Ani Difranco - Used Car (Bruce Springsteen cover)

For cheering up, this: http://www.youtube.com/watch?v=wsqgM4pZy4s

and Pamplemouse does some awesome covers. It's kinda what they do. Youtube it!