Spotify - Map shows when two people play same song at same time
SoundCloud - Enjoy music & follow favourite artists
yungcloud - "the world's leading underground music streaming service."
SoundClick - SoundClick is a music-based social community.
Artrezor.com - New beta social network for sound lovers, including waveform player and uploads. And it's free.
Zoff - Collaborate on a live music and video playlist with your friends.