I use a lot of instant death rules. (I'm a bastard, what can I say.) It varies, but anything like buildings falling on you, armored cars running over your head, high-end lasers hitting you in the face, a gauss rifle or assault cannon shot to the face at point-blank range, somebody shooting/stabbing you in the eye when you're unconscious constitutes an instant death, and so on.
I know it doesn't apply to combat, but I also prefer rollplaying to die rolls when it comes to social stuff.