Thanks skip. I'm having very good luck with MusicBrainz Picard
. I have it set to download only album art at 250px and to name the art "cover." It replaces the current artwork of the album's MP3s and adds a cover.jpg the the folder. Oddly, it added a cover that's 500x500px, despite the options I set, but the cover still works on the CZ (art is only 61kb). 100% success rate so far, though I've only tried three albums so far.
It has plugins and scripting, so hopefully I can get it to do automated batch tagging.