I found out about last.fm last night, and have been toying around with it right now. Basically, it works like Pandora, only last.fm's software shadows your media player, copying the songs you're playing at that moment. Then it makes radio stations based on your listening preferences, or you can make a custom station.
One of the neatest features is a sidebar code that allows people to view or listen to what I've recently played. So for the one of you who asked me to write more about music, this is a way for you to find out where my tastes lie, for yourselves.