I'm sure it's bad form to mention a feature from another tagger and request it here, but here goes!
I wanted to start using the Compilation (TCMP) tag and its proper use is to use a tag of "1" to designate that the album is a various artists compilation. While researching this particular tag, I discovered a tagger called TagScanner. It's a pretty nice program, but I much prefer mp3tag. One nice feature that it has is a simple checkbox labeled "Part of Compilation". If you check the box, it adds a "1" to the TCMP tag.
I know it's not a big deal to just type a "1", but it might be more intuitive for users if you could just check a box!