Wired reviews MP3 tag editors for Windows, Linux, and the Mac.
The best MP3 tag editor I've found is amarok, which is in most ways the best MP3 player I've found. It's the only editor I've used on Linux where you can do something like take an entire album by "-gershwin-" and change it to "Gershwin", so it fits in with your other Gershwin album correctly.
The only use case not covered is to take a bunch of MP3s and guess the tag attributes from the filenames. You can do it one at a time, but there's no "perform on all selected MP3" option for that functionality.