For a while, I was collecting a bunch of Titan's 3" vinyl figurines. I've got a ton of Doctor Who ones as well as some from Buffy the Vampire Slayer and Ghostbusters and 1 from Alien.
I've got a bunch of DVDs, including nearly all of the classic Doctor Who, a tricky feat since a lot of it is out of print now. I've got complete sets of the Jon Pertwee, Tom Baker, & Colin Baker years. I've got all of the surviving William Hartnell stories except for "An Unearthly Child." I've got all of the surviving Patrick Troughton episodes except for "The Underwater Menace, Part 2." I've got all of Sylvester McCoy's stories except for "The Happiness Patrol" & "The Curse of Fenric." My biggest gaps are in the Peter Davison years, where I'm missing 6 stories-- "Kinda," "Snakedance," the Black Guardian trilogy, & "The Awakening."
I have 4 or 5 different models of the Delorean from Back to the Future at different scales.
I still have a bunch of my old Playmates Star Trek action figures from the 1990s. (If only I had kept my old action figures from The Real Ghostbusters and Teenage Mutant Ninja Turtles, I could have made a decent amount reselling them to Toy Anxiety.)
I've never been much of a comic book guy before but I have collected every issue of Spider-Gwen.
I have a few autographed photos-- Nicholas Brendon, Charisma Carpenter, Felicia Day, Alexis Denisof, Michael Dorn, Claire Kramer, Christopher Lloyd, James Marsters, John Rhys-Davies, Richard LaParmentier (who signed it "Imperial officers do it while they're choking"), and the entire cast of Cinematic Titanic.