1. An easier way to sync to gCal directly from iPhone via a gCal sync button. Or have an option in settings to turn on/off gCal.
2. Integrate iPhone contacts.
3. Auto complete for faster & less typing.
4. Integrate GPS for use with an address / location field to warn you if you are near the location specified in this field if the action of the task is set.
Don't get me wrong, I think Toodledo is by far the best todo app for my iPhone but I noticed these additions in other todo apps and they would be extremely helpful especially on the fly gCal sync option for manual syncing with Google Calendar. This alone would be extremely useful.