One of the most influential video games ever would have to be Pac Man. It's design seems charmingly simple now, but it's broad-based appeal remains even today as virtually every gaming platform offers a version of the game. An almost overwhelming amount of interesting trivia can be found in the
Wikipedia entry on the game and its' history. I didn't know that the original title was Pakku-Man, which was changed to Puck Man, and then to Pac Man, out of fears that arcade vandalism would quickly turn Puck Man into something less wholesome. A few video links reflecting the influence our little yellow friend has had:
Pac Man PrankPac Man: The MoviePac Man: The CerealPac Man GenerationPac Man Vs. TetrisMexican Pac Man