I recently tried a piece of software called TuneUp which is an add-in to iTunes, it is a very intelligent bit of software that listens to your tracks and identifies them by their acoustic properties, not existing tag information. If your in the UK then this is a lot like the way Shazam works to identify songs currently playing.

This means that even if you have MP3's with no tag information what so ever, there is a chance that it can find the song from it's acoustic database and return information to tag the file with. It was a bit strange with a few tracks, it would match 9/10 tracks to the correct album but the last track would be the correct track, however it would think it was on a different album for some reason. This may be because I was mainly using compilation albums rather then Artist albums.

The demo of this software has a limit of 100 songs, this can be quite useful if you only have a few tracks that are out of shape, otherwise you can buy a Yearly license for $19.95 or a Lifetime license for $29.95, however you can only install this software on a maximum of 2 computers "ever", this seemed a bit odd to me as I do upgrade and rebuild my PC quite frequently and it wouldn't be much use after 6 months.

It is certainly a different way to do it then to use freedb.org or some other similar DiscID to tag information service.