Torchwood would be an interesting case; I actually keep a rec list of "in another fandom, this would be crack, but here..." fics I've turned up in my travels, because I'm still waiting to run across a story that would manage to look out-of-place considering the premise of the actual show! (I mean, when you can go "Um, and Ianto turned into a dolphin...", and this makes perfect sense, well, let's just say I'd like to see a troll try to keep up...)