first off try over in the video game section. You'll have better luck there as this side is board game stuff.
Tomorrow I'm leaving for an expo tomorrow as an exhibitor
The best I can come up with is trying out steam and looking what games have leaderboards, showing that they have kinds timed trials of levels that people compete on. Bit trip runner and joe danger are first that comes to mind.
good graphics since that's part of what I'm showing.
There it gets a little tougher perhaps a raceing game? there are some very nice ones out there. Maybe mirror's edge? I think it has race challenges. Portal might work, maybe mortal kombat....thats the best I can do with the little to go off of.
what are you doing/presenting? whats the game there for? what do you mean playable on pc, like a laptop? why are graphics a concern? why is this important if you don't have an option by now?