I use Clutter to get artwork for iTunes. Clutter fetches the appropriate artwork and then the user can add it to his library via a menu command -- but Clutter can't add it automatically.
This AppleScript automates this process. It reads each track for a few seconds, gets the artwork, and then adds it to the Library.
Simply quit the script to terminate.
[robg adds: If you have trouble with this script, you might try changing the number in the delay 7 line -- increase it to give Clutter more time to find the covers.]
Mac OS X Hints
http://hints.macworld.com/article.php?story=20050930153429385