I'm surprised Pacific Coast Highway hasn't made the list. That would have been a pretty memorable first for anyone. As mentioned, Sizing Up was my first. (Although perhaps not technically... I bought a Colt film, got it home and it would not play. So I took it back and grabbed the other film that had caught my eye: Sizing Up. -And boy, was I glad I did!!!)
Pacific Coast Highway was the first gay porn I saw. In a theatre, on vacation in New York, when the theatre district was run down as hell and porn shops abounded. The street scene was scary as heck at the time. I felt like a country mouse. But I had to see it and my boyfriend gave in to my request, er -'begging.'
It scorched my poor little brain. The sex was so hot. I'd never even thought of or saw rimming before that movie. I was a bundle of ragging youthful hormones. Literally squirming in my seat watch this larger than life projection of gorgeous cocks, ass and bodies.
As people have mentioned, those price points were outrageous. Far above what straights paid for their porn. I understood the market was smaller, but I always felt we were being taken to the cleaners for no good reason other than greed.
It was a golden age. Who knows what the next wave will bring.