Turntable.fm is a brand new social music service that launched in June of 2011. It has quickly gained a lot of traction among the tech elite but I think this site has the potential to be HUGE. It's a terribly addicting service that allows you to listen to music in a social way with friends. The game mechanics also make for quite a sticky service that makes it hard to pull away. I personally haven't been this excited about a site since Twitter back in 2007.