How about discogs.com? Quite an excellent database with covers with very well documented database API: http://www.discogs.com/developers/ http://www.discogs.com/developers/re...e/release.html
Got already three albums (out of 8 I copied to the phone) which covers the player cannot find. Obviously I will attach my own cover.jpg in the future, yet a properly complex cover database would surely be a nice feature making the player even better.