Dabbleboard is an awesome online whiteboard tools that turns your random mouse scribbles into perfect shapes.
For instance, if you like to add a rectangle or oval on to the dashboard, just draw an approximate sketch with the mouse and Dabbleboard is smart enough to recognize that shape. See this demo video.
This whiteboard application is great for brainstorming sessions as well because multiple people can simultaneously work on the some drawing over the Internet.
There’s an option to insert images on the drawing canvas so the tool could be used for annotations as well. Other than that, you may draw flow charts, org charts, mind maps, floorplans and even web comic strips (like xkcd) with Dabbleboard.
Simply brilliant and the price is just right - $0.