This might be of limited use, given that most of our readers are, I'd guess, iPhone users rather than iPhone designers. But if you find yourself mocking up iOS apps in Photoshop often, then Dev Rocket might be just for you. It's a Photoshop plugin that makes it easy to layout and mock up iPhone app interfaces in Adobe's popular photo editor, automating canvas creation, quickly saving various clips that app developers can use in their programs, and it will even keep two layouts saved at the same time and synced, for Retina and non-Retina Displays.
It sounds powerful, and for the right designer and Photoshop user, it could save a lot of time. Dev Rocket is available now from UIParade's website, for $10.