Call of Cthulhu table-top RPG stuff.
Lovecraft, Clive Barker, and other horror fiction.
I also have a large vintage sci-fi book collection and an extensive occult library.
Warhammer 40,000 Tau (about 5,500 point army) and Necrons (about 2,500 points).
And I make (very good) wargames scenery as well as horror props so I'm ending up with a growing collection by default.
Minerals/rocks and gemstones.
I still have quite a bit of Dreamcast and N64 stuff too.