More than I care to count although some I picked up mainly for reading anyways
Let's see what I do remember
Pathfinder, Star Wars Saga Edition, Nightbane, Paranoia, GURPS, Teenagers from Outer Space, several variants of DND, Arcana Evolved (other than playing a Spryte Wood Witch ina mixed D20 game one year at GenCon), Mage Ascension (though I ended up selling that last year), Werewolf, Wraith, Recon Deluxe, Robotech, Teenage Mutant Ninja Turtles, and probably at least a half dozen I'm not remembering.
If it weren't for a couple online games, Mutants and Masterminds would be on there..funnier considering I own nearly every book of the series.