1. Create a one bag solution. I normally use Bagnon, but I think if nUI had it's own Bag Management then that would be cool.
2. Wintergrasp timer
3. Currency tracker -- Honor points, Marks, Gold, etc.
(This might be part of the ammo/gold tracker in to-do list)
4. XPerl Unit Frame integration would be cool. I used to use XPerl a lot because of the ton of information in a small frame.