Partyhero - Pass your friends the aux!
Spotify - Map shows when two people play same song at same time
Join My Playlist - Listen to music live together with your friends in Spotify.
Last.fm - The world's largest online music service. Listen online, find out more about your favourite artists, and get music recommendations, only at Last.fm
OutLoud Social Jukebox - Control the music with your friends in real-time
SoundCloud - Enjoy music & follow favourite artists