G.D. Spradlin as General Corman in Apocalypse Now before debriefing Captain Willard:

"Roast beef, and usually it's not bad... to save a little time, maybe we could pass both ways..."

"It's a trap!"

Christopher J. McGarvey wrote:Most of Withnail & I would go in this category.

GETINTHEBACKOTHEVAN!

"I'm walkin' here, I'm walkin' here!"

"Uh, well, sir, I ain't a f'real cowboy. But I am one helluva stud!"

"John Wayne! Are you tryin' to tell me he's a fag?"

Most of The Big Lebowski dialogue does it for me.

Jack Nicholson's "How do you like it?" when his wife skims his novel in The Shining.

From The Big Sleep:-

Bacall: "...speaking of horses, I like to play them myself. But I like to see them work out a little first. See if they're front-runners or come from behind... I'd say you don't like to be rated. You like to get out in front, open up a lead, take a little breather in the back stretch, and then come home free...."
Bogart: "You've got a touch of class, but I don't know how far you can go."
Bacall: "A lot depends on who's in the saddle."

"This is T. Chalky's dead. Now, I'm comin' to get you honky ass"

Just about anything from the end of Superfly would work as well.

"My name is Horace" from the tail end of Monster Squad is also pretty great.

"Son, you got a panty on yer head" - Raising Arizona

"8 year-olds..." - The Big Lebowski

"I can't see shit can you?" - Cannonball Run

"The lady, she-a gonna have a baby!" - Smokey & The Bandit II

'Shag off you creeps'

The bit in Made in Britain where they explain to Tim Roth that he'll end up in prison if he continues with his life of delinquency, and he replies:

"Sounds Great! When do I start?"