MusicBrainz Picard is a cross-platform application written in Python
and is the official MusicBrainz tagger.

Picard supports the majority of audio file formats, is capable of
using audio fingerprints (AcoustIDs), performing CD lookups and
disc ID submissions, and it has excellent Unicode support. Additionally,
there are several plugins available that extend Picard's features.

When tagging files, Picard uses an album-oriented approach.  This
approach allows it to utilize the MusicBrainz data as effectively
as possible and correctly tag your music.

WWW: http://musicbrainz.org/doc/MusicBrainz_Picard