a white, blackboard thing (also known as a whiteboard ;P), would probably be too shiny and give a big hotspot.
I'm either going to paint the chimney breast matt/satin white, or a pale icestorm, or try a frame with screen material in it, which I can hang up to view on.
Then when not viewing, i'll either pull it down, or put a print on the other side and turn it round! Might be a bit big though.