easytag is a nice GUI tagging tool that can use the filename to divine a meaningful tag and also rename files and directories from the tag information. This can save you a lot of time if you're willing to trust it's "smartness". I suggest copying a small section of your collection to a scratch directory and trying it there before you trust your entire collection to it, but that's just my conservative nature.

tagtool is another GUI application with very simlar features. You might try it out as another option.

musicbrainz is a whole system for tagging music files. There are tools that they provide to allow you to use their system, and their are also libraries that allow you to write your own musicbrainz enabled apps. The musicbrainz system is very interesting, they use something called TRM IDs (not sure what it stand for). These IDs are like acoustic fingerprints for music. When you rip a CD to MP3 or OGG it's pretty easy to see how the application could request the track information from some service like freedb.org and fill this info into the tag for the files, but if somehow a pre-encoded track name "track01.mp3" has worked it's way onto your hard drive, how can you automatically get the song information? We'll if someone has provided the TRM acoustic fingerprint of that song to the musicbrainz network, then whatever app you're using can find that fingerprint by comparison and tag you file appropriately. It's damn near magic! I say all of this without ever having used this technology at all. It's just a little too smart for someone like me just yet.

lltag is another one of those smart taggers like the first two that use the filename to divine a meaningful tag, but this app is a command-line app.