Personally, The Rocky Horror Picture Show.
I knew it was going to be quite the experience before I went for the first time‡ but it was so much fun I had to keep going back bringing friends each time.
It’s still a fun tradition to do though we haven’t done it since last year, we’re probably going to try and go again in a few weeks.
‡ I had seen it many times before going to see it in theaters for the first time.
Spirited Away. Before it won the Oscar it was in limited release in the US. A friend drove me nearly three hours to the closest showing. After the Oscar it came to most theatres. I took other friends to see it on two separate occasions.