Windows only: Free application MetatOGGer is an advanced MP3 (and OGG Vorbis, FLAC, Speex, Musepack, Windows Media, WavPack and Monkey's Audio) tag editor that can automatically tag your music by creating audio fingerprints and comparing them with online database, MusicBrainz.
And while MusicBrainz already has its own dedicated application for this (the previously mentioned Picard), we've always found Picard to be a little clunky. MetatOGGer, on the other hand, seems quite a bit more user friendly. Likewise, MetatOGGer can automatically search out and add lyrics to your tags from web site LyricWiki.
This one didn't make our list of the six best MP3 tagging tools, but then again, we didn't even know it existed. And while it may not be as efficient as something like MP3Tag, it does show a lot of promise.
MetatOGGer is freeware, Windows only, requires .NET 3.5 SP1. If you give it a try, let's hear how it worked for you in the comments.