I ran across this cool site, Audioscrobbler, the other day where you can send in what you are listening to and then it will track statistics and create a profile of the music you listen to. Mine is here, I’ve just started submitting stuff so it’s not very detailed.
To make it work you just download the plugin for your media player, install it and then keep playing your music. =) They have plugins for iTunes, Winamp, XMMS, Windows Media Player and several others. After you start using it, they process your submissions and make recommendations and matches with other people who have similar tastes in music. Apparently, the process works similarly to how Amazon.com calculates suggestions for you based on things you have purchased.