MusicBrainz.org falls under the category of "useful apps", making use of acoustic signatures on your song files to match against its database and retrieve reasonably accurate tag information.

You can search the database from the web, or better yet, download a tagger utility either for Mac or Windows.

iEatBrainz, the Mac utility, operates wonderfully, correctly identifying and semi-automatically correcting a number of mp3 files in my collection that were consistently misidentified by Gracenote (see screenshot)