emusic.com

I used to use it, but the bands were too obscure, even for me. :) It may have gotten better in the time since I last used it. I tried it back in 2007, I think, so lots could have changed, though I get the sense it's still quite 'fringe' in selection - great for people who like to go deep into a genre, rather than stick to what's generally 'popular'.
 
While I like the price of $0.49 per song, my major issue with it is there is no Christian music...

Lot's of older stuff, like Hendrix, Zeplin and others but not much I listen to today...