Invented by the so-called father of video games Ralph Baer and Howard Morrison (with a little software help by Lenny Cope) MB's Simon game was released in 1978. Impressively and despite its simplicity it turned out to be a huge success, survived well into the 80s and got itself countless re-imaginings and sequels. Weird, I know, especially considering Simon's gameplay consisted of replicating tunes played by the machine in a way that has plagued too many an adventure game.
Anyway. Simon was an interesting and successful digital novelty/game thingy that's definitely worth owning, if only for nostalgia reasons. This boxed Simon auction on eBay sounds particularly interesting too, as the seller ships worldwide and is giving away the complete boxed game.