I collect, or used to, TCGs. Now not so much, but when I was little nothing made me happier than rectangular pieces of cardboard. I never threw away any of it, so I still have it all. I have TCGs of Pokemon, Digimon, Dragonball Z, Magic the Gathering, Magi Nation, Cardcaptor Sakura, Yugi Oh, Werewolf: The Apocalypse, Neopets, Legend of Zelda: Twilight Princess, and World of Warcraft.
My cumulative collection of the above is enormous. Now I still get Pokemon cards as gifts from relatives and friends, and I buy World of Warcraft cards for the occasional gamble.