MOG
As social networking sites become bigger and bigger people have a harder time finding new friends or meaningful stuff to share. As a result there is an increasing number of niche or topic focused sites coming on to the scene. The latest, MOG, is music focused and includes obvious but useful features like favorite artist this month or most recently played track. But what makes it slick is the MOG-O-MATIC plugin that trolls your iTunes library to compile all this information automatically. Of course there are also manual features like photo albums and blogging, but I find the tools for discovering new music most useful. MOG is still in private beta, but if you ask around you should be able to find an invite.
