I have a database inventory of 543 RPG items, which, while not in the thousands, is enough that I'm not going to list them all here.
I've sold a fair amount of stuff over the years in times of financial stress and I also lost a significant collection of AD&D 2nd Edition, BECMI, Palladium, and Old World of Darkness stuff back in 1999 during a move. Oh, and about half my collection of print Dragon magazines were stolen back in 2004.
Anyway, what I do have now (just the highlights)...
Vampire: The Masquerade 20th Anniversary edition
Werewolf: The Apocalypse (2nd Edition)
Mage: The Ascension (2nd Edition)
Wraith: The Oblivion (2nd Edition)
Changeling: The Dreaming (2nd Edition)
Mummy: The Resurrection
Vampire: The Dark Ages
Werewolf: The Wild West
Mage: The Sorcerer's Crusade
Scion: Hero
Monte Cook's World of Darkness
Dragon Age RPG
True 20
Blue Rose
Mutants & Masterminds (2nd Edition)
Pathfinder RPG core book (plus lots of more)
D&D Basic (the original Red Box)
D&D Rules Cyclopedia
AD&D 1st Edition core books (plus a couple more)
AD&D 2nd Edition core books (plus several more)
D&D 3.0 core books (plus everything non-setting specific)
D&D 3.5 core books (plus lots and lots more)
D&D 4th edition core books (plus quite a bit more)
D&D 4th edition Essentials (all of it)
D20 Modern
Nightbane
Dragon Magazine 309 to 359 (missing a couple of issues in the 310s and 320s)
And a great big box full of maps and dungeon tiles.