If you develop iPhone Apps and want to demo them onstage you could simply use the Xcode Preview app (or whatever it is called). But here is an app that will give you that real Steve Jobs magic feeling of showing REAL products in REAL time.
Now all you need is jaibroken iPhone, your finished iPhone App and DemoGod. Using a Wi-Fi connection you will be able to demo your iPhone app on the iPhone while its screen will be duplicated on a larger screen behind you. All you need to do is install ScreenSplitr and Demogod.
This is a Mac only solution and in beta but it will rotate with the iPhone’s accelerometer and works good enough to use in a demo.
Check out this video demo of DemoGod: