A few days ago I presented you with an online mock up tool. Today I want to include a link to Yahoo’s Design Stencils. You have more than just iPhone in here but these are great if you use OmniGraffle, Visio and so on.
Remember to not worry so much about the asthetics but concern yourself with the actual idea and workflow. We (or other mobile and iPhone development companies) can help you make it “look pretty”!
Direct Link: http://developer.yahoo.com/ypatterns/about/stencils/