I'm surprised no one has mentioned Chris Cornell. Not necessarily my TOP choice but some of the Soundgarden stuff is fairly impressive. Damn, I love Otis Redding's voice/music. If you are going to mention him though, it is hard to ignore Bill Withers. I'd put him WAY up there.

If you haven't heard "The Gossip" from Portland, you should check out the lead singer. She farking rocks. Kinda like a Stevie Nicks that could kick your ass.