From The Good, the Bad and the Ugly:
There are two kinds of spurs, my friend. Those that come in by the door; those that come in by the window.
Also:
You see, in this world there’s two kinds of people, my friend: Those with loaded guns and those who dig. You dig.
Gunfight at the O.K. Corral:
The men best able to testify about my aim ain’t around to comment
Support Your Local Sheriff:
It’s bad enough to have to kill a man without having to listen to a whole lot of stupid talk from him first.
From The Outlaw Josie Wales
Lone Watie: How did you know which one was goin’ to shoot first?
Josie Wales: Well, that one in the center: he had a flap holster and he was in no itchin’ hurry. And the one second from the left: he had scared eyes, he wasn’t gonna do nothin’. But that one on the far left: he had crazy eyes. Figured him to make the first move.
Lone Watie: How 'bout the one on the right?
Josie Wales: Never paid him no mind; you were there.
**Lone Watie **(after a very, very long pause): I could have missed.
**The Outlaw Josie Wales **is the Buckaroo Banzai of westerns when it comes to great lines.
“We all die. Just a question of when.” - Hombre
“Every gun makes its own tune.”
-The Good, the Bad, and the Ugly
Great lines in Cowboy, with Jack Lemmon:
Tom Reese: And all that hogwash about horses! The loyalty of the horse! The intelligence of the horse! The intelligence? You know a horse has a brain just about the size of a walnut. They’re mean, they’re treacherous and they’re stupid. There isn’t a horse born that had enough sense to move away from a hot fire. No sensible man loves a horse. He tolerates the filthy animal only because riding is better than walking.
AND
Shane: So you’re Jack Wilson.
Wilson: What’s that mean to you, Shane?
Shane: I’ve heard about you.
Wilson: What have you heard, Shane?
Shane: (Lowers voice and delivers this line unlike any way he’s talked in the movie before) I’ve heard that you’re a low-down Yankee liar.
Wilson: (Smiles, long pause): Prove it.
Tombstone, after Kurt Russell smacks around Billy Bob Thornton: "You gonna do something, or just stand there and bleed?"
And one of my favorite scenes from Outlaw Josey Wales is when the bounty hunter comes in and recognizes Wales, and Wales talks him out of throwing down with him, and the bounty hunter walks out of the saloon. A few seconds later, the bounty hunter walks back in the bar and says, "I had to come back." To which Wales responds, “I know.”
I quote Doc Holliday from Tombstone all the time:
“I’ll not be a part of that.”
“I’m afraid we must redefine the nature of our association.”
John Wayne in McLintock! (1963):
It’s all in the delivery. To see it written it’s a very ponderous “Fill your hands, you son of a bitch!”.
But, hear it spoken, and it is the much lighter “Fill youre hands, you sonofabitch!”
“I call that bold talk for a one-eyed fat man.” ain’t bad, either. 
The Searchers:
Ethan:
I found Lucy back in the canyon.
I wrapped her in my coat.
Buried her with my own hands.
I thought it best to keep it from you.
Brad:
Did they…
Was she…?
Ethan:
What do you want me to do? Draw you a picture? Spell it out?
Don’t ever ask me! As long as you live, don’t ever ask me more!
“I’m your huckleberry.”
No indeed. I use that one around the house from time to time.
“Best shot I ever saw”
“The worst. I was aiming for the horse”
Chamlee: I don’t like it, no sir. I’ve always treated every man the same: just as another, future customer.
Henry: Well in that case, get that hearse rolling.
Chamlee: I can’t, my driver’s quit!
Robert: He’s prejudiced too, huh?
Chamlee: Well, when it comes to a chance of getting his head blown off, he’s downright bigoted.
Russell - “Hey! I’ve got a question.”
Grimes - “Yeah?”
Russell - “How are you going to get down that hill?”
Yeah, that was good!