AirSketch App - $9.99
Air Sketch turns your iPad into a wireless whiteboard! You can annotate PDF documents and pictures live. If your laptop is plugged into a projector then your audience will see your annotations as you freely move around the room. Click here to learn more about Air Sketch.
You can also use Air Sketch peer to peer with a computer via an ad-hoc network with a WiFi hotspot is available. Click here to learn how.