iEatBrainz - Stupid Title, Clever App.

I've been using iEatBrainz for a while now, and it does a really good job of tagging all those unnamed or badly named tracks in iTunes. It uses audio matching to check your songs against a CD databse called MusicBrainz, and then updates your iTunes library. Unfortunately, it's Mac only at the moment, but there seem to be some other interesting apps for Windows users over at the MusicBrainz products page.