LOTR fandom is actually pretty good and has fewer arguments over canon policy or who can beat up who than most. A lot of fandoms fall apart into warring camps which I never really understood in the first place.
Oh man, I have so many fandoms.
Buffyverse, Firefly, Doctor Who, Harry Potter, Game of Thrones, Castle, Lord of the Rings, Zelda, Fable, Hunger Games, Veronica Mars, Bones, Stargate, Battlestar Galactica, Studio Ghibli, Charmed, Dark Angel, Dead Like Me, Dollhouse, Gilmore Girls, 4400, X-Files, Mario....
I wouldn't join the Sonic fandom if I were you. It's like the Zelda fandom, but much more hilariously bad & more vocal.
As for what I like: Pokemon, Zelda, My Little Pony (I'm not one of those fans, by the way), Digimon, Kirby, Mario, Kingdom Hearts, Gravity Falls, Ratchet & Clank, Frozen, How To Train Your Dragon, The Lion King
I'm the kind of person who really dedicates herself to just a few things and doesn't spread out too often. A few of them are Skyrim, Dr. Horrible's Sing-Along Blog, and Super Smash Bros. I was also in love with MLP and Pokémon for a while, but I'm really not that into those anymore.
My two biggest fandoms, however, are Zelda, of course, and... Danny Phantom. Zelda's obvious -- I've loved it for forever -- but my obsession with DP is relatively new and kind of unhealthy. It's... sort of a guilty pleasure. The show is so stupid at times but it never fails to make me smile (unless it's Kindred Spirits, because that episode is absolutely terrible). I'm also hopelessly in love with DP fanfics; I literally wake up early in the morning to read them. And I think it's also the reason I haven't been as involved in any of my other fandoms lately, haha, except SSB.
Which fandoms do I like? Ew. None. Fandoms are ****ing scary. There's, like, shipping wars and people diagnosing fictional characters of mental disorders... it's just constant angers. No.
Which fandoms am I in? Several. I usually lay low because I'm so tired of people being ebola. Though, like, a chunk of this stuff is probably too obscure to be classified as having a fandom (which is probably for their own good). Here's some notable fandoms I'm in: Animal Crossing, Avatar, Attack on Titan, Blood of Eden, Big Hero 6, Ergo Proxy, Hamtaro, Harvest Moon, Legend of Zelda, Pokémon, ЯEBIRTH, Rune Factory, Star Wars, Super Mario, YUREKA.
But yeah, I pretty much dislike the majority of the fandoms I'm in. People are terrible. You see the worst of them when you spend a fair amount of time on tumblr. I would not recommend it.
I'm kind of moving away from my fandoms and that makes me really sad. Need a better work-life balance!!
But...my biggest ones are Zelda, Fire Emblem (only with a select few things tho), MLP, I dabble in Pokemon and Kingdom Hearts, Lord of the Rings, sort of dabble in Pokemon, sometimes venture into Star Trek, will read Pirates of the Carribean, favorite stories in Naruto, FMA, YuGiOh, and Harry Potter for old times sake.
Any other Sherlock fans in the house? Adore Sherlock and the fandom is crazy fun!