WeAreHunted was the best, until Twitter put a bullet in it's head. I think it was reincarnated as wonder.fm, but never really seemed to regain the mojo from those early days...
It worked off of music blogs, with the idea that at any given time, some collection of blogs/bloggers would have found the next big thing.
The founder is an interesting guy who is currently currently providing VC for a bunch of ideas, one of which is using AI to make music. Their demos are pretty interesting.