I have 4 different game series I'd probably be considered "Hardcore" fan of. They are:
Lunar - I have all the English released games in the series. I also both the Japanese and English versions of the Sega CD versions and PSX versions of Lunar 1 and Lunar 2. I also have both of the art books made for Lunar, and two different mangas from the series. I also have the Ghaleon punching puppet promo thing.
Tales of - I own most of the English released games in the series, including some of the Japanese ones. I have 4 art books (Symphona, 2 different Symphonia anime artbooks, and Legendia). I have a Zelos figurine, and I've watched all the anime related to the series (Phantasia, Eternia, Symphonia, and Vesperia), and read quite a bit of various manga in the series.
Castlevania - I own every English released Castlevania game but Legends, Dracula X, and Lords of Shadow. I used to own LoS, but I ended up selling to go towards another game. I have a Japanese Judgement guide and the English Symphony of the Night guide, 2 posters from Nintendo Power (Dawn of Sorrow and Castlevania III), an Alucard figurine, the 8-bit Simon figurine, the PoR anniversary box, and the two volumes of the Curse of Darkness manga. I also have a Saint Germain shirt I bought off of Ebay, lol. I'm sure I'm forgetting stuff, but whatever.
Devil May Cry - I own all the games in the series, including the new DmC. I have all the novels, manga, and anime. I also have a display box for the new DmC.