When you tell itunes to find your cover art, it misses lots of albums that presumably are not on amazon.com where it looks for cover art. So what do you do?

Well you can do a google image search for your album and then drag the resulting image onto your empty ‘playing now’ artwork.

Or you might try these sites:

http://www.rateyourmusic.com (you will need to register)

http://www.slothradio.com/covers/

http://www.cdcovers.cc/