I've been using a great little productivity app on my iPhone and iPad to keep focussed on tasks.
Its called 30/30 - the app is developed by Binary Hammer and it is just beautiful in its simplicity.
The app uses a gesture based interface and its a breeze to add tasks, allocate times, prioritise your tasks - and allow yourself to stay 'in the zone' for the allotted time to Get Things Done. An absolute technophobe will be able to use it.
And, yes, its free! There are some in-app purchases available if you want any extra task icons etc ... but thats just window dressing in my opinion. I highly recommend 30/30.