I've never attempted to design an iPhone or iPad app, but I theorize these stencils and sketch pads would come in handy. UI Stencils has a line of sketch pads and stencil kits intended to aid in the process of conceptualizing and creating iPhone and iPad apps. Given the time of year, these would make great gifts for any iPhone, iPad, Mac or technology enthusiast.
Regardless whether I would use these for their intended purpose, I think they look completely awesome. The company has really thought through the design of these tools as well, including pixel measurements across the top of the stencils, as well as the physical locations of important device features, such as the mute button. Very cool.