For everybody with a Last.fm account: LastGraph lets you get a nice visual graph of what you’ve been listening to. Above is just a part of the ocean of music I’ve listened to. You can see it all by downloading this PDF file.
A little tip: when asked if you want to be notified by e-mail when your graph is done I’d choose yes if I were you. Mine took quite a long time. Maybe it’s because I wanted to see all the music that I’ve ever listened to, which breaks down to over 200 different artists and over 400 unique songs. ;)