Dammit, now I'm curious. A fast 15 minute count reveals 138, although some might count as supplements. Physical copies only:
D&D
Aces & Eights
Adventure!
Amber (sold it)
Ars Magica
BESM
Burning Wheel (gave it away)
Call of Cthulhu
Champions
Changeling (gave it away)
Cyberpunk
d20 Modern(gave it away)
Deadlands
Dogs in the Vineyard
Dread
Exalted (gave it away)
FATE (gave it away)
Fiasco (tempted to buy but balked at the price tag)
Game of Thrones (gave it away)
Gamma World
Grim Tales
GURPS
Kobolds Ate My Baby (gave it away)
Mage (gave it away)
Marvel Superheroes
Mutants & Masterminds (gave it away)
Northern Crown (gave it away)
Paranoia (sold it)
RIFTS (gave it away)
Rolemaster (gave it away)
Rune (gave it away)
Savage Worlds (gave it away)
Scion (gave it away)
Shadowrun (gave it away)
Sidewinder Recoiled (gave it away)
Skull & Bones (gave it away)
Spaceship Zero
Spycraft (gave it away)
Thieves' World (lost it)
Top Secret SI
Traveler (gave it away)
True 20 (gave it away)
Vampire (gave it away)
Warhammer Fantasy (gave it away)
Werewolf (gave it away)
World of Darkness (gave it away)