I currently use (on Windows) 2 tagging programmes:

MP3 Tag & Rename
This is great for scanning a few folders and file/tag modifying, but it's not a DB so anything that you want to do on large numbers of files is pretty tough (I have 25,000 odd files)

MP3 Manager
Development on this stopped in 2002, it does everything I want that Tag & Rename doesn't, it's only flaw is that it doesn't really work (very well) with ID3 v2 tags. There's an open source product based on this around (written in Python) but it's for Linux.

Any ideas on a programme that'll do what I'm after? I've played with Helium in the past and have tried Media Catalog Studio & MP3 Boss today.