Board Cam is an app that turns your iPad into an enahanced document camera. You can perform and annotate live demonstrations, pull in and annotate images, or use a a whiteboard. I’ve made a video to show off some of the features.
The most powerful feature of this app for me (other than laserpointer fingertips, obviously), is the ability to easily record and post what you’re doing. The free version allows to project an annotate live, but has a limited recording length.
There are also ideas and tips on the Board Cam website.
This post has some great ideas for how to use the document camera (with or without the Board Cam app): 5 Awesome Things you can do with an iPad and an LCD projector