My top 3:
Apocalype Now
Kilgore: Smell that? You smell that? Napalm, son. Nothing in the world smells like that.
[kneels]
I love the smell of napalm in the morning. You know, one time we had a hill bombed, for 12 hours. When it was all over, I walked up. We didn't find one of 'em, not one stinkin' dink body. The smell, you know that gasoline smell, the whole hill. Smelled like... victory. Someday this war's gonna end...
[Kilgore unhappily walks off]
Dr. Strangelove
General Jack D. Ripper: Mandrake, do you recall what Clemenceau once said about war? He said war was too important to be left to the generals. When he said that, 50 years ago, he might have been right. But today, war is too important to be left to politicians. They have neither the time, the training, nor the inclination for strategic thought. I can no longer sit back and allow Communist infiltration, Communist indoctrination, Communist subversion and the international Communist conspiracy to sap and impurify all of our precious bodily fluids.
The Third Man
Harry Lime: Don't be so gloomy. After all it's not that awful. Like the fella says, in Italy for 30 years under the Borgias they had warfare, terror, murder, and bloodshed, but they produced Michelangelo, Leonardo da Vinci, and the Renaissance. In Switzerland they had brotherly love - 500 years of democracy and peace, and what did that produce? The cuckoo clock.