Stargate SG-1 is one of mine. Buffy and Smallville were my starter fandoms. Glee was huge for me. And now it's Kingsman. Nothing else has struck me recently.

My other big thing is Yuletide. I love the challenge of writing for different fandoms that I wouldn't otherwise have a chance to write. Nothing warms my heart more than getting a comment on a fic I wrote many moons ago that's been found.