I am an avid and longtime Toodledo user but recently discovered a handy feature in an iOS app called "Alarmed" that absolutely love. Basically it keeps sounding the reminder "alarm" on a reoccurring basis until the task is marked as completed. This is essential because I often get the alarm, but I'm busy at the current moment (driving, meeting, etc) then forget to go back and complete the task. Alarmed also has a useful way to "snooze" tasks for a specified amount of time when want the alarm to sound again.
I would definitely be willing to pay extra for this feature! If you have any questions please let me know.