MusicBrainz Picard is a cross-platform (Linux/Mac OS X/Windows) application written in Python and is the official MusicBrainz tagger.

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

Go to http://musicbrainz.org/doc/MusicBrainz_Picard to download for free.

The two plugins i found most useful were
Last.fm Tags – Use Last.fm tags as “genre” (This may slow down auto tagging significantly but does a good job)
Cover Art Downloader – Downloads cover art for optional tag embedding and/or saving as a separate image file (works fast and seamlessly)
you can download these plugins plus much more here .