This site has an algorithm similar to the amazon/netflix system of recommendations. You put in a band (or a movie), and it spits out a map of related musicians that you probably would like. It's a nifty way to identify groups you may not have heard of (their depth is pretty decent; I've only managed to stump them a few times). Alternately, it's a great way to play the 'six degrees' game - how else can you get from Belle & Sebastian to Warrant in five bands?