Jonny Cash - Hurt
Easily for me. Cash has tons of fantastic covers, and I usually like Eddie Vedder/Pearl Jam's covers of songs as well. Hurt is probably the best song I've ever heard, though. There's so much emotion put into it, unlike anything I've heard.
Originally Posted by the_thatguy /img/forum/go_quote.gif Jeff Buckley - Hallelujah
Probably my current favorite cover, either that or Funeral for a Friend / Love Lies Bleeding by Dream Theater, but Jeff Buckley changed and improved the song whereas Dream Theater changed an already awesome song to a different style IMO. I don't really know many covers though.