Just spotted this post by Scott Hanselman about the iTunes Album Art Importer which automatically searches Amazon.com for album art for music in iTunes. The application is written using the .NET Framework 1.1 so that is required for it to run.
I had been wanting to write something like this using the iTunes API but I never got around to it. Great to find that the program was made for me :)
Download iTunes Album Art Importer.
Disclaimer The opinions expressed herein are my own personal opinions and do not represent my employer's view in any way.