MP3Tag is great! The more I use it the more I find great features. I only recently discovered the $left function, so I can easily put files in my letter alphabetized library just where I want them. Great!
m:$left(%artist%,1)\%artist%\%year% %album%$num(%track%,2) - %title% or other easy syntax choices for Classical or Various...
One thing that I constantly find myself wanting to do though, is click on a track, and find that track in the Filesystem - ie: open a Windows Explorer window with the folder. Like Picasa does for photos, or iTunes (ick) does for music files. This is particularly relevant if I received a batch of untagged stuff, and I'm slowly picking through it and tagging it properly. I've got thousands of files opened at once in a bunch of subdirectories.
The other thing is a way to make covers consistent per album. Just like you can set the Album and Artist for an album, I want to make one of the covers that a track has the cover for all the tracks. I found I can copy the cover I want to use from the one track, then select all the tracks, and paste it, but it's nowhere near as easy as setting the artist and album title for all tracks.
Thanks for listening. Sorry if these topics already came up, but if they did, count this as another vote for them.