FIEND.fm - "Hot or Not" for music discovery: 2 hrs of tracks in 2 mins
Momixa - Pick two songs and get the perfect mix
Music Suggestions Ninja - Enter an artist's name & find similar, lesser known artists
Liveset Database - Database site with tracklists from Dj sets
RYSE UP - Connecting up-and-coming artists with the world's top talent
Cymbal - Music discovery powered by friends