I used to collect comic books, specifically X-Men and Wolverine, also a fan of X-Files and Star Trek: Voyager, but never posted to any sites for these. If we go by the OP’s standards, I am a fan of the Harry Potterverse, MST3K, and anime and manga in general; more specifically, I am a fan of Sailor Moon, Bleach, and Naruto (my current favorite to the point that I am making several AMVs and made my daughter a TenTen costume for a convention last year).
If “writing and posting fic” counts as posting to a board, NCIS, The West Wing and House. If commenting on written fic counts, add Supernatural, Stargate Atlantis and Law & Order SVU.
The largely female, creativity-driven form of media fen/fandom is a whole other ball of wax, methinks.
“Circle” Fandoms (ie, Fandoms I get into, leave for a while, then get back into again eventually): Pirates of the Caribbean, X-Men, Pushing Daisies, Sweeney Todd, Lost
Past Fandoms: Moulin Rouge (well, actually the fanfiction aspect of it, since I loved the look of the movie, if not the plot) and Rent
I’m counting fandoms that have been the source for fanfics I’ve read as well as messageboard posts.
X-Files, Buffy, Angel, Firefly, Dollhouse, Farscape, Star Trek (all), Harry Potter, Terry Pratchett.
The X-Files fandom was HUGE for years and I spent my life on the X-Files official site messageboard messing around, discussing stuff and reading/commenting on fanfic; sometimes I’d have 12 different WIP fanfics on the go at a time. I made quite a few friends there who are still my friends ten years later even though the site closed years ago and we all hated the last two seasons.
Most of my fennish behaviour pre-dated teh internets.
However, I still participate with some fellow old pharts and discuss Doc Savage, Barsoom, and what is now considered vintage Science Fiction. I am currently working out why John Carter never seems to have noticed the H.G. Wells Martians (part of the background for a friend’s stories).
Also Silver-Age DC comics.
Not really any, nowadays. Once upon a time Trek; and Animé/Manga long ago enough that subcategory fandoms had not taken form yet.
Nevermind.
LOTR, most definitely. used to post on The One Ring.net; 1st read the books over 40 years ago.
Others to varying degrees (and I refuse to be ashamed) : David Cook; Pirates of the Caribbean; Johnny Depp; Dr. Who; Blake’s 7; Guiding Light; Lost; House…
no I have no life, sadly
I’ve written fanfic and been unhealthily obsessed with two fandoms: Harry Potter and The Office.
I’ve never missed a single episode of Survivor since the first season, but I don’t know that I’d consider myself part of the fandom…I just like to watch the show and occasionally read the forums. I might have posted way back in season two, but I don’t really remember, so I don’t think it counts.
I currently have no pop culture obsessions, which is a change for me. I think it might have something to do with becoming a parent. Maybe once my daughter and any future children get old enough to give me more free time, I’ll find a new show/movie/actor/novel to dwell on.
My husband and I met because we were both Kate Bush fans and have traveled to three fan conventions, one in Canada and two in London. I also did 95ish% of the html and 98ish% of the graphics on the biggest Kate Bush fan site Gaffaweb (be kind, hey, it was all done in early 1996). I’m not really involved in the fandom anymore but she’s still my #1 musical goddess.
This woman’s status as a deep underground cult artist with an elite worldwide fan base pretty much exists because of me (she’d say that too, she has said it). I’ve seen her live 24 times, and 22 of those times involved traveling, mostly to the east coast, and thanks to my long-suffering husband (who likes her fine, but isn’t a fan) videotaping while I blissed on the music, fans old and new can see over 50 live clips on YouTube. I didn’t start her mailing list, one of, if not the, oldest continually-running music mailing lists on the internet (it started in 1991 and is still going strong) but I turned the woman who did start it onto her. I’m no longer on the list but I’m fiercely proud of it.
I would have called myself a huge, HUGE (Peter Gabriel’s) Genesis/Peter Gabriel fan, but I was never really involved in the fandom, though another fan turned me on to Kate Bush, and a Kate Bush fan turned me on to HTR.
Back in the day, Twin Peaks.
Same here. Good old alt.fan.twin-peaks eh? People involved with that group were much more informed and aware of all the references than the average viewer. We lived in Kansas City where there was no public access internet, and had to call long-distance to “The World” in Boston to check our mail and read the newsgroups. There was hell to pay with our phone bills but it was worth it. When we moved to Chicago we joined a fan viewing group too.
That’s either pretty awesome or pretty odd. Regardless, I salute you.
And if you ever decide to web-publish the Dr Who/Bonanza crossover, let me know. The mind reels.
Officially, as in its several fansites still remember me, Firefly. Took a (spiritual) load out of me a long time ago.
I guess by the OP’s standards, I’m only a Buffy fan.
I see some of you have outed yourselves as fanfic writers. You’re all hereby invited to participate in this thread. 
*** Ponder
The only real fandom I became a part of was for the show Homicide: Life on the Streets. I went into it late, then watched the past shows and became incredibly into it. Actually traveled to Baltimore the last week of filming for the series in hopes of watching filming but weather changed the schedule and we* missed it. Still had a great time and saw James Yoshimura (Squeeeeeeeeee!)
*With a female friend I’d met from the alt.tv newsgroup for the show. She was older than I, and an oldschooltype fan. Utter Trekker. Told me she would always HATE NBC b/c they’d cancelled the show. I’d learned of fanfic, but she was the one that showed me the TONS of fan created slash that she had collected.
By the ‘posted on a message board’ standard:
Penny And Aggie, Sluggy Freelance, and uh… Raine Dog? I’m really more of an anti-fan of Raine Dog, but I have posted about it. I’m also an anti-fan of Eragon, having posted quite a bit on a forum somewhat dedicated to criticizing it.
Other than that–Harry Potter, I guess. Attended opening nights.
I’m a MSTie, going back to '95. Even have my info club membership, and a chunk of Deep 13’s wall.
Oh, and I once attended an all-day online MSTing/“Riffing” session when AMC first ran all the Heisei Godzilla films, one Halloween.
There were a good number of us when it started, in the morning. At the end, there were three of us left. I am honored to have stood by my comrades to the very finish.
Did you ever post to rec.arts.tv.mst3k.misc? I was a regular poster there in the late 90s.
Not with any regularity—I was on the AOL boards (Heck, this is even the same screen name I used back then!). We probably met a lot of the same people, though!
By that standard: none.
If you’re willing to include USENET then I’ve done my time as in Babylon5, MST3k, and more generally comics, anime, and SF.
I’m not really sure what the standard is for someone who enjoys something but can’t stand fan communities. I’m a “fan” of many things but don’t care to be part of “fandom”.
Currently: Star Wars, and D&D.
In the past: Star Trek (I actually founded a fan club for a member of the production staff on TNG and Voyager, and that staffer and I were profiled in Star Trek Communicator magazine).
My wife is really into various fandoms, and is a fairly accomplished fan-fic author. She currently focuses on Supernatural and The Magnificent Seven, but past obsessions included Pirates of the Caribbean, Invisible Man, X-Files, and The Sentinel.