A few suggestions would be:
1) Duplicate tasks from one day to the next. Example: If you were to make a task for feeding the cats every day you could have that be duplicated from one day to the next. In other words, repeating task support.
2) The ability to move an item from one list to another (like you can do with the web interface of Google Tasks).
3) Arrows to move the target date for a task
4) Support for different Widget sizes (larger widgets and smaller widgets)
If I think of any others, I'll try to remember to post them... maybe I'll make a task to do it so I remember!
-Benjamin