IDroo - A shared whiteboard for use by multiple Skype-users simultaneously. Features
NoteBookCast - A real time shared whiteboard in your browser, teach, explain, sketch. For work, study, fun.
drawonthe.net - Draw on the . net is an online, multi-user, drawing website.
Twiddla - Mark up websites, graphics, and photos, or start brainstorming on a blank canvas.
Whiteboard Fox - Simple Online Whiteboard
CoSketch - CoSketch is a multi-user online whiteboard designed to give you the ability to quickly visualize and share your ideas as images. No registration or plugins required.