If I shouldn't count Mister Roger's Neighborhood, then I suppose my first fandom must have been Star Trek: the Next Generation. Although I am the right age to have had profound experiences of Back to the Future and Teenage Mutant Ninja Turtles and so many other things, it was TNG that gave me a framework to see myself, and to think about values and hopes. There was room for someone like me in the world of TNG.
I found all kinds of aesthetic fulfillment and allure in so much cheap SciFi besides, and in the Rust Belt gothic of Forever Knight, but TNG was home. It made sense, then, that as my sense of humour started to look for a way to come with me, I found myself deep in the arms of Red Dwarf. That show shaped a crucial period of my life in a big way, though I wish it could have offered me a bit more of an escape. I suppose part of its charm was in how small its universe was, though. Just people, nowhere, nowhen.
As an adult, I have gone through waves of Babylon 5 and Star Trek: Deep Space Nine, which reflect different parts of me that have been important in these other stages of my life.
Music is a huge part of how I experience and think about myself, too, and deserves its own commentary elsewhere. Still, I am undeniably a fan, in some profound and slightly embarrassing way, of Pet Shop Boys and The KLF and Cocteau Twins. There are a lot of other musical acts who warrant special mention, from Soda Stereo to Machines of Loving Grace to VNV Nation and Caifanes and Depeche Mode and Thomas Dolby and Gary Numan, but they are too numerous to list. What about Underworld, and Deacon Blue, and The The, and Xymox, and Cabaret Voltaire!? Too numerous, indeed.
I have given numerous talks to church groups about fandom, about how self-organizing communities with a common set of metaphors can be places of support and development, and can act together in profound ways. I also got to give a talk at a furry convention on how I see the cultures of furry and otherkin communities as being very much like religious identity in the era of religious choice, which was absolutely wonderful. I could say similar things about Aikido as a community of practice, too. It's good to let ourselves enjoy and share things which feel meaningful to us. It's a fine thing to be enriched by fandom.