Mp3tag is hands down the best audio file tagger for Windows. It is incredibly powerful, supports multiple filetypes and makes managing metadata in your files a breeze. It's also completely accessible. You can get it at: http://www.mp3tag.de/en/download.html
An honourable mention for foobar2000 if you happen to use that, which can also manage file tagging duties quite admirably. Note that Mp3tag and Mp3/Tag Studio are not the same thing, probably goes without saying but I figured I'd mention it. -- James Scholes http://twitter.com/JamesScholes
