It would be nice to see more objects added to the list of dialog objects. I know that this has been discussed numerous times before, but I figured I'd just say that since the Rich Edit Boxes have finally been added, it's nice to have. I would much like to see Rich Edit controls extended, for things like Font & Colors.
Progress bars, treeview, listview and comboviews would also be a great touch! Not sure how practical or how difficult these are to implement, but still worth waiting for