last.fm
There's an online music service called "last.fm", which is an online database of the music people listen to. You can find people who listen to similar music, and through them find other music you might be interested in. They provide a nice rss feed for your recently listened tracks. They also provide information about what your top tracks/artists are, overall and weekly. This information is updated every once in a while, rather than constantly. It also takes a little while to get a big enough database for the data to actually mean something. I listened to a bit of Nick Drake to see what I thought of his music, and he's now one of the top artists on last.fm, whereas I've hardly listened to him ever and still prefer a lot of other music that isn't even on the list.
Anyway, I wrote/stole a php script to parse that rss feed and display it on my web site. That's where the link goes.
This service seems to be very interesting. I signed up on a whim, not because I though it was going to be extremely useful, but because it was a neat idea. Now I'm there. You might try it out too, if you want.