Good software for tagging mp3 file is hard to find. There are lots of choices but I still haven't found a single program that would do everything I need from tagging program. Some are good when comes to editing, others are good when renaming files or parsing filenames and others do good job searching databases like FreeDB.
I mostly use long defunct Media Tagger and have Mp3tag for backup and querying Amazon for tag info. I have tried to use MusicBrainz Picard, but it's just too complicated and slow to process file like that.
But it seems there is a light at the end of the tunnel. On of my favorite web places - Last.fm - is developing tagging service/application. But they need your/our help - the are asking everyone to calculate fingerprints of their music files, where they are tagged or not, they ask to include even badly tagged files.
Just download their app, select your music folder and let it run. It will take +-5 seconds per file so leave your computer running when your not using it and you'll be done. The app even lets you stop and continue later, so you really don't have any good excuse not to contribute.
Oh, your files will not be modified at all, you are just sending fingerprints and metadata so last.fm builds it database before next steps of the project.
Read more at Last.fm - the Blog.