First off, I have to say that you have made an awesome program which blows all the competition away, including the ones that cost money. And I hope it will be possible for you to keep this application free.
Now, I have two requests:
Being able to choose which buttons are shows on the toolbar. Very practical since I only use a few of them and there's a lot of buttons there. Shouldn't be very hard to make.
Extended tag information. Like original artist, copyright, encoded by and all the rest. Most players can show these and it would be nice to have them here, I don't use them myself all that often, but still.
Small things, but these would make this the perfect application, or very close to it.
Would you believe that I haven't been able to find another tag editor that can jump from one songs title (or anyting else)to the next by pressing enter while editing the tag in the file list?