I bet a
Commodore KIM-1 playing MicroChess would be an eye-catcher (assuming
 you couldn't get a Commodore Chessmate). 
 I've always been pretty impressed with the 1979 Atari VCS "Video Chess"
 (
http://en.wikipedia.org/wiki/Video_Chess).  A fairly capable chess
 opponent (even if it does cheat at higher skill levels :)) written in 4K
 rom, with access to only 128 bytes of RAM.  Not sure if it's a great
 museum exhibit, but it's pretty easy to track down & set up... 
 
Oh, that *is* a neat little game as well.
My favourite "not sure why but it's neat" cart on the VCS, though, is
BASIC Programming. Neat. Not practical, but neat.
--
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http://www.cameronkaiser.com/ --
  Cameron Kaiser * Floodgap Systems * 
www.floodgap.com * ckaiser at 
floodgap.com
-- You told me to get a life. May I take yours? -- "Scream V" -----------------