Here is a nice portable projector for your iPhone 4/4S.
As usual Jetdaisuke gives an entertaining review. Here are the key points:
- bright at 35 lumens
- maximum projection size 1524 cm (yes, centimitres)
- 120min battery life
- works as a OHP (overhead projector) with your camera
With external speakers you can add sound to your presentations.
Check out his youtube video (sorry, in Japanese, but you can get an idea of the product).