Openwhyd - Collect and Share the tracks you love.
Spotify - Map shows when two people play same song at same time
Zoff - Collaborate on a live music and video playlist with your friends.
SoundCloud - Enjoy music & follow favourite artists
Ampache - Web ( HTTP centralized ) based audio/video streaming application
Music Smasher - Find any song. Music Smasher searches Spotify, Rdio, SoundCloud, Bandcamp, and YouTube.