There certainly are many relevant quotes in McCarthy's novel. Since you do not specify what themes or questions the quotes should illustrate, I will include several that are especially meaningful in relation to the theme of human depravity, one of the most conspicuous in the text being:
1. What do you say to a man that by his own admission has no soul? Why would you say anything?
The previous quote, stated by Sheriff Bell at the beginning of the novel while reminiscing about the only boy he ever sent to the gas chamber at the Huntsville prison, begins to weave into the narrative a religious discussion about the human soul.
CITATION: McCarthy, Cormac. No Country for Old Men. Knopf Doubleday Publishing Group, 2007, pp. 3-4.
2. Somewhere out there is a true and living prophet of destruction and I dont want to confront him. I know he’s real. I have seen his work. I walked in front of those eyes once. I wont do it again. I wont push my chips forward and stand up and go out to meet him. It aint just bein older... And I think a man would have to put his soul at hazard. And I won't do that. I think now that maybe I never would.
This quote comes from the same chapter, or part, as the first one, and here Bell discloses his acceptance of both the fact that the world is under dire threat by the forces of evil, incarnated in the Satan-like character of Chigurgh, and that he is too much of a coward to confront him.
CITATION: McCarthy, Cormac. No Country for Old Men. Knopf Doubleday Publishing Group, 2007, p. 4.
3. You cant go to war like that. You can't go to war without God.
Bell's father criticizes the US involvement in the Vietnam War without the proper moral justification for its intervention and sees that lack of legitimacy as the reason for the defeat. War, by the way, is a pervasive theme both in No Country for Old Men and in Cormac McCarthy's fiction at large (especially Blood Meridian)
CITATION: McCarthy, Cormac. No Country for Old Men. Knopf Doubleday Publishing Group, 2007, p. 295.