http://beets.radbox.org
http://beets.readthedocs.org/en/1.0b10/index.html
Beets is the media library management system for obsessive-compulsive music geeks.
The purpose of beets is to get your music collection right once and for all. It catalogs your collection, automatically improving its metadata as it goes using the MusicBrainz database. (It also downloads cover art for albums it imports.) Then it provides a bouquet of tools for manipulating and accessing your music.