Mp3tag is a super-sweet and lightweight little app for cleaning up the mess you've made of your ID3 tags. But don't take my word for it: in the words of a user, it's "simply indispensable." Now, I'd disagree with that if I was using a music jukebox like MediaMonkey that supplies its own excellent editor, but for iTunes users--and I used to be one--I'd be hard-pressed to get by without it.
The autotag feature comes from a rarely-wrong pedigree, sourced by FreeDB, Amazon, or discogs. If you don't like the results from one, simply flip to one of the other choices. Besides checking and correcting song tags en masse, the lightweight app recognizes your massive song library in a matter of minutes. It took less than 5 minutes to scan mine, which has more than 8,000 tracks.
Mp3tag allows batch or single edits to effect such changes as case changing, autonumbering, 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 offer the program up for international use, and a Favorite directory setting makes it easy to return to your My Music folder, or wherever you store your tracks.
I wasn't enamored with the interface, which was a bit too simplistic and could've been clearer. It's not hard to navigate once you get used to the busy Toolbar and using mouse-over labels to identify button functions, but bigger buttons or at least more easily identifiable icons would make it a smoother ride. At worst, the UI will slow you down, but in no way should it stop you from using this top-flight MP3 tag tweaker.