I'm nearly finished preparing 12,000 songs. :-\ Right now I have to go through my album art and make sure one cover shows for multiple songs instead of that small glitch that shows multiple versions of the same cover for multiple songs. Pain in the ass!
Do you have any suggestions other than the iTunes sites for the artwork? So many of the albums either don't seem to get attached to the artwork when I go through the process or they are missing the artwork complete.
Amazon wasn't bad. Honestly, Media Monkey saved my tail when it came to album art. Plus there's a program called TuneSleeve that did a decent job just finding basic album art, didn't consider the song, just the artist. But Media Monkey more than did what it had to for me.
Every night I work on the Album art for my library. I like to find the highest resolution version of the album art I can. I then crop it as necessary so there aren't any ugly borders as well as color correct it. It is time consuming, but I figure it is worth it. I may get an AppleTV sometime down the road and then I will really be able to appreciate the high res artwork.