Just playing around a little bit of iOS prototyping tools, found Keynotopia application quite useful.
Keynotopia costs $0.99 on the app store and the templates cost around $9 each. Most of the buttons, scrollable menu, pop-up text box designs etc. are readily available which makes it easier to design. The app itself opens the prototype as a PDF. So A PDF builder such as Keynote or OpenOffice.org will help in building the prototype. All the UI elements are linked together as a hyperlink. So every object or page can be linked to the next resulting slide using a hyperlink. This is all saved as a PDF and you can add this PDF to the app on iTunes. I just loved the simplicity and design of creating prototypes. Quite a useful tool.
As I was going through some prototyping tools, found another tool called Interface which seems very easy. No hassle of PDFs , hyperlinks or slides and costs $9.99. This tools lets you create iPhone prototypes on iPhone. The Interface demo video is worth a watch. They say the ‘Live Preview’ feature shown in video is no longer available due to Apple’s SDK restriction, so not sure about what part of it you can build using only iPhone.
Some more useful tools here –
21 prototyping tools for iPhone app development