dBpoweramp lets me easily edit ID-Tags. Love it. But the choices of tag fields are more appropriate to music than audio books, and I'd like to add several fields to the "Add" button drop down list. Yes, I can type them in, but then sooner or later I will vary what I type and end up with mixed up tags. Much rather control what's in the list and choose from that list. (FWIW, the fields I'm looking at adding at this point are "Narrator", "Series", and "Series Index". Though "Author" is more appropriate than "Composer" or "Artist" for the author.)

This could be controlled with a simple XML or INI file, or even be smart enough to pick up from any fields I've already added and automagically add them to the list.

I'd also like to see the editor recognize values I've put in fields and auto-fill the field as I type, or from a dropdown list, but this is less important.