Due for iOS is the reminder app I've been looking for since I started using my iPhone on June 29, 2007. Super simple to set up reminders, well-designed, and very annoying... in a good way.
An unsolicited 'Highly recommend!'

iPhone, Blackberry, Pre... whatever you're sporting... what apps are on YOUR home screen?
An oldie but a goodie. Ryan Bates' (of Railscasts.com fame) excellent remake of David Heinemeier Hansson's original 15 minute Ruby on Rails blogging app demo.