Intellivision: Space Battle, circa 1978 (And I still have it) (Edit) I got the year wrong, I looked it up and Space Battle came out in 1980, either way it's ancient.
Christ I'm old...
(Edit) Technically the first game I ever played was on this dinosaur of a machine called a Telstar Arcade which came out sometime around 1976 and was this weird looking 3 sided pyramid that had some paddles for pong, a light gun and a steering wheel/gear shift.
(Re-Edit) Holy crap I found the telstar: Check it out here: http://www.pong-story.com/coleco_arcade.htm and I was wrong, it came out in '77
So yeah, I've been a gamer since before most of you were born...
Now I need a drink...