FIEND.fm - "Hot or Not" for music discovery: 2 hrs of tracks in 2 mins
Gnoosic - Even if you don't know what you are looking for - gnod will find it.
Music Suggestions Ninja - Enter an artist's name & find similar, lesser known artists
Musicroamer - A visual Pandora for discovering new music
RYSE UP - Connecting up-and-coming artists with the world's top talent
TasteDive - TasteDive recommends similar music (musicians, bands), movies, TV shows, books, authors and games, based on what you like.