When I was a kid, we had a family friend who was a wargamer and a prolific military miniatures painter and collector. He really opened up my ten year old eyes to this great hobby (1983 or so).
My father went away for some business meetings, and his friend Rich, was with also. My dad told me about this great game he played, and he went to his suitcase and pulled out a new copy of Cry Havoc!
We played a couple of games and I was instantly hooked! This became my gateway-game for the hobby of wargaming.
Cry Havoc! is a skirmish level medieval warfare game. The maps were wonderful, and the full color counters and easy rules made it a perfect learning tool. Due to the scale of the game pieces, it made it an easy conversion for miniatures!
Unfortunately this game is no longer available, but there is an online version available here.
If you are a fan of Cry Havoc, this is a great site! And if you've never heard of it, this is a pretty good introduction to the game.