Oh, that would be awesome, if you're looking for ideas. I'd make sure that it could be done without dates, too.
And one of the MOST requested plugins - fixes to WordPress - whatever requested around here repeatedly is a NEXT/PREVIOUS post tag/plugin that keeps the next and previous posts within the same category - and if I'm not really asking too much - allows controlling which categories if the post is listed in more than one - like parent, subcat, and other cat...maybe four categories - or only the parent category. Maybe too complicated, but it would be a dream come true for me.
Just having a simple next and previous that stays in the same category would be a dream totally.
But I'm happy enough with the first plugin you've done. Amazing Wonderful...I'm going to run out of endorsing adjectives soon!
As for the rest of us....don't you feel a little guilty that you aren't contributing a little more....makes me feel guilty! This is what makes this whole thing so amazing!