I was reading this thread on The Forge, which was linked to in Ben Lehman's Blog, and got inspired by it to come up with a quick outline for a Sorcerer setting. I don't know what it is about that game that begs for it to be modded to other settings.
Anyway, the idea?
Sorcerers are post-war veterans. Demons are their training, their altered mindsets, their ability to kill, and their weapons. Are Demons entities apart from this? Perhaps. This is something that could be explored in game, particularly if you wanted to go for a more surreal Jacob's Ladder feel rather than something more Ramboesque. Humanity is empathy and the ability to see others as human. At Humanity 0, you simply can't interact with people anymore - people are mere objects, and those who stand in the way of even the smallest of your goals are likely to be killed without thought.
Source material? First Blood, Commando, Die Hard, Lethal Weapon, or anything where someone resolves conflicts by relying upon combat training and/or a willingness to step outside of the normal rules of society.