I learned about sketchcast.com from the Chronicle of Higher Ed’s “Wired” blog. Apparently some teachers are using this tool to some effect in their courses. Here is the nickel tour:
You draw in a small window using a pen tool, text tool, and eraser tool. You can record your voice along with your drawing or sketch. Then you click “publish” and an animated movie of your drawing process is published. It is quite easy. You can then send the web address to anyone out there in the world.
This basically is like an online whiteboard. It takes a few minutes to get used to drawing with a mouse, but with a little practice it is quite easy!