Long ago, I signed up on last.fm and downloaded the AudioScrobbler plugin for iTunes, which plugin listens to what I'm playing in iTunes and sends a report of it the last.fm web site. Then I promptly forgot about it. A year and a half later, it's compiled quite a musical dossier on me: 10,300+ tracks listened to (that's about 18 per day), my most listened to track is A Dream by Cut Copy, and my 10 most listened to artists are Ladytron, Boards of Canada, Fischerspooner, Bloc Party, John Digweed, Daft Punk, Royksopp, Pixies, Radiohead, and Sigur Ros.
Even longer ago, I used the dearly departed Kung-Tunes to place a list of my recently played music on kottke.org. Thanks to the last.fm API and a gently modified version of this PHP script, that list is back; you can find it on the front page of kottke.org.