Last.fm is “the social music revolution”. It works by letting you “scrobble” your music to their service, which basically means telling them what you’re listening to. Then, they use that data to “make personalized recommendations, connect users who share similar tastes, provide custom radio streams, and much more”. After a few scrobbled songs, your personalized radio station should provide you with a constant stream of free, enjoyable music. It’s open source, and currently only available for Mac users, though you can get some of the functionality on your PC with a Skype plugin; so if you always find yourself trying to find new music that suits your tastes, maybe it’s time you join the revolution.