OK, related
question - what's the most interesting graphics display system 
 Didn't someone have a scheme for hooking up an Etch-A-Sketch to a system?
 This would probably be back in the S-100 days, but I seem to recall a
 magazine article about it. 
 
Milton Bradley "Big Track" toy "military vehicle".  Programmable
similar
to "turtle graphics".  Duct tape a pen to it.  Try to find the
"trailer",
since it adds a Pen-up/pen-down capability.   I think that Ciarcia may
have once done an interface to it.