About 20ish, I believe, not counting PDFs.
D&D (BECMI, 1E, 2E, 3E, 3.5, 4E)
Dark Heresy
Dragon Age RPG
Mutants & Masterminds (2e)
True20
Blue Rose
Pathfinder
Nightbane
Ninjas & Superspies
Rifts
Teenage Mutant Ninja Turtles & Other Strangeness
D20 Modern
Vampire: The Masquerade
Werewolf: The...