I've been tagging my flac's with mp3tag for some years now, and it is the best tagger I have tried by far! The only thing I've been missing is a practical way to save the values for e.g. style, mood, theme, location, label etc in lists. Also lists for artist, composer, conductor, producer etc would be practical, to keep spelling consistent.
I've tried to use sample files and to use Actions, but those solutions weren't well suited for this purpose.
There are several requests here on the forum for customizable drop-down lists in the Tag Panel - while this would also suit my needs, the solution seems to displease those who want to keep the current functionality of the drop-downs.
So, to be able to have value lists while keeping the drop-down feature untouched, I have the following suggestion:
In addition to the drop-downs in the Tag Panel, there could also be buttons for pop-up windows. These pop-ups would contain customized lists with values for the tag in question. For example, when you click the button next to Style, a window with the values for Style pops up. In this window list, you would select one or multiple values to be added to the tag.
I think this solution would satisfy those of us who have been wishing for value lists, without touching the current functionality of the drop-downs.
I've photoshoped a picture to illustrate my suggestion (note the extra buttons in the Tag Panel).