I think for me a combination of old cartoons and the Super Top Trumps card game. My older brother had both the heroes and villains decks which we'd cut together for an uber-game.
After that, the late '90's/early 2000's wave of films (though at the the time the first Blade was released, I'd no idea that it was a Marvel property - my knowledge was that lacking).
An old work colleague of mine introduced me to the Punisher at around the same time that the first TPB of Ennis' seminal MAX run hit the shelves, so serendipity there.
My ex-girlfriend triggered my interest in the main 616 universe back in 2006 when she introduced me to the first ever Sentry series on a hunch that I'd appreciate it. I pretty much followed the character from there, from team to team. My interest in Marvel comics immediately wanes during the years that the character is inactive. I feel a certain kinship with Mr. Reynolds, having suffered similar afflictions.