Sawbuck Gamer, the AV Club's bi-weekly collection of cheap or free games, mostly for browsers and iPhones. It's where I found Canabalt (which I still <3) and there are a few others I've tried which are neat. Dig through the articles and you'll probably find something fun and unusual.
People know that Halo 2 will be on PC eventually. My wife's been playing the hell out of this on our Cube. Since the survival-horror genre is the only major reason we got a Cube in the first place, this helped justify the purchase a bit more.