My #1 favorite website for high quality album art is
AlbumArtExchange.com. I was hoping to see the site implemented into MusicBee as an available source for tagging album art like Amazon, Discogs, google, etc. are used now.
I know that the site doesn't have an available API, but it seems to have a search feature which could be treated similarly to how Google is currently in the auto-tagger. The only problem I can see is that it requires a login to the site's forum to continue using the site without having to enter capcha codes every x amount of times you click on an image.
Let me know if you have any questions regarding the request. Thanks for taking a look!