Atari 2600 -- I wish I'd kept those cartridges!
Heh... I installed Stella just a bit ago and played through a bit of "Adventure" -- ah, the mighty block, armed with his golden arrow of dragonslaying... those were interesting times. My wife, who never had access to an Atari, had NO IDEA what the possible appeal was (she's a more modern gamer, but at least she's a gamer, so I can't complain).