Notification Actions in the iOS app would allow users to take immediate action on tasks rather than having to tap multiple times. I suggest Complete and Postpone as the options. Here are some examples comparing the current behavior of Remember the Milk to Clear:

[Lock screen](http://i.imgur.com/QGdwyZ9.gif)
[Notification Center](http://i.imgur.com/0HJc03M.gif)
[Home screen](http://i.imgur.com/Et6jnj6.gif)

See the iOS HIG document about Notification Actions here: https://developer.apple.com/library/ios/documentation/UserExperience/Conceptual/MobileHIG/NotificationCenter.html