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.
Unfortunately, I've had technical issues with Amarok taking up a lot of CPU just sitting there doing nothing, and the way it plays MP3 with separate engines isn't working well for me.
It's a pity, because it also has what is rapidly turning into a killer feature for me: The ability to rate things on a five-star system, in half-star increments. I know that iTunes and some other players can do that too, it's just that I thought it wasn't an interesting feature and didn't care. But I've realized that once I've got things rated, then I can do things like "delete everything with less than two stars", which will probably cut the disk space my collection takes down by perhaps a third at no musical cost to me.