It took me a while but I just love mp3tag on Windows to tag mp3s. The free Tritag on the Mac is Ok, but doesn't add artwork at all. And adding artwork doesn't really work well with iTunes, sometimes it seems to get into the MP3 and sometimes not. Even when you manually add, it doesn't.
And the best thing about mp3tag is that it is very smart about taking tags from a filename. Maybe The Tagger is the answer.
Deadbeat Software has released The Tagger, its new MP3 and AAC tag editor for Mac OS X. According to the developer, The Tagger features support for batch editing of audio files and a wider range of ID3 tags than iTunes, search and retrieval of tags from Discogs, the ability to remove hidden personal data from iTunes Plus files, and more. The Tagger requires Mac OS X 10.5 or later and sells for $29; a free 14-trial is also available.