Fetch Art for iTunes is a small program that will fetch album art for one or more songs using Amazon's XML interface, allow you to preview the art that was found, and add the art you want to iTunes. The program is controlled through the iTunes Script menu: once it is installed, album art can be downloaded by selecting one or more songs in iTunes and choosing "Fetch Art" from the Script menu. It doesn't require an account to get art and works from any country.
What's new in Fetch Art for iTunes
Fixed a problem introduced with iTunes 10.2 where iTunes handles picture files differently now.
Slight performance increase in handling larger groups of files.
Changed the warning dialog from over 500 music files to over 1000. Let me know if it's fast enough that I should increase that even more. It tends to slow down with more music selected.