Openwhyd - Collect and Share the tracks you love.
PlaylistMap - Connect with Spotify playlist curators from around the world
Zoff - Collaborate on a live music and video playlist with your friends.
Undrtone - Social layer on top of Spotify and Rdio from Scott Vener
SoundClick - SoundClick is a music-based social community.
SoundCloud Charts - The most played tracks on SoundCloud this week