I was looking for a radio station to listen to tonight and ended up at Last.fm, powered by Audioscrobbler. In the words of audioscrobbler.net, "The Audioscrobbler system is a database that tracks listening habits and does wonderful things with statistics", which is to say that it can do a pretty good job of guessing what kind of music you like, and its accuracy improves the more it's used. Last.fm has done a great job of hooking into the recent wave of social networking-based web services that are storming the net by tapping into audioscrobbler's service, while working as a regular radio station by having music labels feed them tracks and cash to run the network. Check it out: Last.fm