So Spaced99 and I were talking about influences on the Lovecraft books thread, and the topic of what turned us into SF/horror/fantasy/monster fans came up. I was born in the early '70s, so it was a pretty rich period for genre stuff — Star Trek and Batman reruns on TV, lots of superheroes and sci-fi shows on Saturday mornings (mostly DC, come to think of it), plus the emergence of video games that were heavy on space imagery, like, well Space Invaders and Asteroids. And of course, the giant 500 lb. gorilla of the SF world, the original Star Wars (which I will never refer to as "A New Hope").
But I think it was mainly just weird random stuff that got me into the genre, like obscure children's books or B-movies or forgotten TV shows. Empire of the Ants was a big one, maybe moreso than George Lucas or Spielberg. And the older I get the more frightened I am to discover that I know most of the dialogue to the Rankin-Bass Hobbit cartoon (no doubt thanks to the LP my parents got me for Christmas). And Yellow Submarine. And STARLOG magazine, which probably did more to build my basic SFnal vocabulary than anything else (and published my one and only letter to a real publication). Though it was almost certainly Alien that cemented my relationship to the genre, more than Star Wars or Close Encounters (which explains a lot).
What about you?