Space Invaders.
They brought an arcade cabinet into the youth club at our school, and it was the first video game I ever saw. Or should I say heard, because I never got to see it for the first few weeks because there was such a huge crowd around it all the time. But when I did get to play it, it awoke the gamer in me.
It was the only experience I had of video gaming for another couple of years, until we got our first home console, the Atari 2600. It had a fairly faithful replica of Space Invaders, which we played to death, as well as Super Break Out, Pac Man and Missile Command. The rest of the games weren't much good, I seem to remember.
I remember being on holiday in the early 80's and encountering Mario Brothers, and not being very impressed with it at the time, preferring Defender, Asteroids and Pole Position.
But yep, Space Invaders was the one for me.