Taggerwocky is an easy to use tag editor for MP3 audio files from Artly There Software. Available for regular PPC MacOS and also Carbon/X.
You need not pay anything to use it. The author will not turn away any donations however, should you feel so inspired, because he has put some good bit of effort into it. :) Worth at least a beer per MP3 edited. Maybe. Your price is a simple email telling the author if it works for you, or not, and any praise or any other life changing comments you may have. Contact the author for distribution information.