Small But Vicious Dog. It's a mashup of BX and Warhammer fantasy. I know nothing about Warhammer fantasy but there are several really interesting subsystems you need to see here. A social status system that affects combat, saves versus poison that have varying degrees of debilitation, and probably the most elegantly simple rules for addiction I've ever seen.
I'm leaving on a trip in a few hours but this has got me excited about tweaking this to come up with poisons, drugs and diseases for my own campaign. I think I'll be able to fit each on a single page or less. And that, my friends, is right down my alley.
p.s.: I think folks could learn a lot from the voice of his rules, too, not treating them as if they exist in a vacuum or as if an abstracted corporate voice is necessarily the easiest to understand.