A month ago I want to the Seattle Mini Maker Faire at the EMP Museum. (March 22/23 2014) and saw several items that interested me.
http://www.marginallyclever.com/shop/drawing-robots/makelangelo-3-complete-kit was one such item. It uses two motors at the top corners of a drawing space to suspend a pen holding device that raises and lowers a marker from the surface.
The most interesting thing mentioned to me was that the top corners could use suction cups and draw an image on a window.