SoundCloud - Enjoy music & follow favourite artists
Openwhyd - Collect and Share the tracks you love.
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.
Music Smasher - Find any song. Music Smasher searches Spotify, Rdio, SoundCloud, Bandcamp, and YouTube.