Doceri turns your Ipad into an interactive white board and screencast recorder. You can download a free trial but the real app costs $30. But it might be worth it. It allows you do what the Khan Academy teachers do, which is to annotate the presentation. For example, lets say that you have an outline map of India and you want to explain the direction of the monsoon winds, you can actually draw arrows onto the whiteboard.
Doceri connects your laptop to your ipad. You can project your laptop and control it from your Ipad.