MP3cddb is a great command line MP3 tool for Unix that renames and modifies tag fields in MP3s, including freedb lookups (as the name suggests).
And a quick look on FreeDB indicates there’s been a big hissy fit between the team members there. Please don’t take away my free lookup service 
Finally on the topic of mp3s, I’ve noticed that Firefly Media Server (formerly mt-daapd) doesn’t like the > character in comments fields (and presumably other fields) in your mp3s.
Popularity: 6% [?]