Cosketch is another whiteboard that you can collaborate on to visualize your ideas and share them as images. The good thing is that you don't have to register or install anything. It works in all rowsers, it's real time, and you can get an embed code for your drawing after you finish.
Color interpretation and meaning presented in a very creative and eye catching way. This site could be used not only in art class, but in small groups or a class meeting/ adviser setting.
Imagination Cubed is a multi-user drawing tool. You can use a pen, stamps, shapes, or lines, or you can type. You can also change the color of the background.