Momixa - Pick two songs and get the perfect mix
BandNext - Discover bands that sound similar to artists you already love with BandNext. A single click saves your results to a Youtube playlist.
Boil the Frog - Create a seamless playlist between any two artists
Spotify - Map shows when two people play same song at same time
Cymbal - Music discovery powered by friends
stats.fm - With the click of a button you'll be logged with your Spotify account and you'll instantly gain access to a valhalla of cool stats and insights.