skrbl - Simple and easy online multi user whiteboard, start skrbl, give out your URL & start working...
IDroo - A shared whiteboard for use by multiple Skype-users simultaneously. Features
Scribblar - Scribblar is a free online collaboration tool that is perfect for online tutoring.
NoteBookCast - A real time shared whiteboard in your browser, teach, explain, sketch. For work, study, fun.
Twiddla - Mark up websites, graphics, and photos, or start brainstorming on a blank canvas.
Wottactic - Whiteboard app for game planning