I was a bit surprised when I stumbled upon this batch MP3 tag editor. People seemed to love it. Not The Dark Knight love it, but perhaps X-Men 2 love it. In the words of a user, it's "simply indispensable." Turns out, you could do much, much worse than Mp3tag if you're looking for a freeware ID3 tag editor.
It comes with an effective single and batch auto-tagging feature, sourced from FreeDB, Amazon, or Discogs. The lightweight application also sports batch and single edits to effect such changes as case changing, auto-numbering, tag and track name flipping, and user-defined actions. There's playlist support and configuration exporting in six formats including CSV, HTML, and RTF. Support for more than two dozen languages offers the program up for international use, and a Favorite directory makes it easy to return to your music assuming you keep all your tracks in the same root folder.
The interface is a bit too simple, though. It won't be hard for anybody to navigate once you get used to the busy Toolbar and using mouse-over labels to identify button functions, but it certainly could be clarified with bigger buttons, or at least more easily identifiable icons. At worst, the user interface will slow you down, but in no way should it stop you from using this top-flight MP3 tag tweaker.