Games - I started with tabletop wargames and roleplaying games in the 80s, stuck to mostly roleplaying games in the 90s (but kept buying the game that was my primary interest during my teens), and transitioned to video games in the mid-90s. My preference is for RPGs and strategy games, with a focus on SF and Fantasy.
Autism, ADHD, Neurology - While the two specific conditions have been a big interest for me, neurology is generally something I research to learn more about the first two things.
Science fiction and fantasy novels - All over these. Everything from hard SF to sword and sorcery.
TV shows - Buffy, Angel, Firefly, Heroes, Battlestar Galactica, Game of Thrones, Doctor Who, Babylon 5, Star Trek: TOS, Avatar: The Last Airbender, Justice League... I tend to focus on one at a time, and cycle through them. I like to marathon an entire series at once (recently did with Battlestar Galactica, Black Adder, and Firefly, and currently doing with Red Dwarf. Plan to do next with Stargate SG-1, Stargate Atlantis, and Stargate Universe, possibly also Xena).
Movies - SF and F by preference again. Action's good, especially Hong Kong style wire fu and gun fu. Give me flying martial artists doing implausible feats any day.
Cats - Cats are a long-term interest.
Mythology - especially Norse and Greek. I love anything to do with the Greek and Norse gods.
Superheroes - comic books, roleplaying games, movies, etc.
Anime - Nothing recent, but stuff like X/1999, Neon Genesis Evangelion, one I'm forgetting that involved a lot of AI and men in black, many I would have liked to watch all the way through but never managed.
Hard Rock and Heavy Metal music - lots of this. I still like it, but not as much as when it was my interest for a good two years.
Most of my interests are sort of hobbyish, but they are rather consuming in their turn.