The Warriors-in the subway scene, where the girl tries to straighten her dress to look as good as the prom queens on the ride, and the guy stops her.
Also, the ending to Pink Flamingos. (sorry)
Rocky Horror Picture Show, The wedding scene. Then the timewarp, unveiling of Rocky and Meat Loaf’s interruption then murder. Brad and Janet’s seduction. Meh, screw it, the whole movie 
True Romance - Sicilians were spawned by niggers.
Pulp Fiction - “Say ‘what’ again!!!”
Mulholland Drive - The man behind Winkie’s.
Lost Highway - Fred Madison meets the Mystery Man. “Give me back my phone.”
Boogie Nights - the pool party scene where Dirk Diggler first meets his new friends, with “Spill the Wine” in the background - just sums up the hipness of the time period perfectly.
There Will Be Blood - something about imbibing a lactose-based beverage?
Mad Max - the opening scene where the car and tanker truck explode in a giant burst of fire, and Max steps out of the car and takes off his sunglasses (the first time the audience sees his face.)
And this one is just a personal favorite of mine because it’s so ridiculous, and doesn’t really qualify as a “best all-time movie moment” but I have to bring it up anyway because of how unintentionally hilarious it is:
The Fly - “we just turned a baboon inside-out…now let’s fuck each other and eat steaks!”
Well, now that I’ve googled it, I know what TKAM means. Is that movie’s title really so well known by its initials that it doesn’t have to be spelled out?
Jaws, I vote for the USS Indianapolis scene.
There are so many good ones in that movie, it’s hard to pick just one. Also :
“We’re gonna need a bigger boat.”
The scene of the Orca going out to sea as seen through a sharks jaws.
At the end of ‘Quigley down under’, Quigley stands over the bad guy after the six-shooter gunfight and says, “I said I never had much use for one. Never said I didn’t know how to use it” in reference to the fact he prefers his rifle and is never seen in the movie using a six-shooter.
Actually, the words just before that are pretty good, too. “This ain’t Dodge City. And you ain’t Bill Hickok” as he adjusts the gun in his belt. The bad guy at that point should have know to run for cover.
Jurassic Park - Tyrannosaurus rex breaks through the fence.
The Descent - Night Vision camera reveals a Crawler for the first time
The Ring - “I *saw *her” (cut to quick scene of dead girl in closet) and also “Why did you do that? You weren’t supposed to HELP her…!”
The Jerk - “He hates these cans! STAY AWAY FROM THE CANS! THERE’S CANS IN THERE, TOO!”
Swingers - Mike:“It says here ‘breakfast anytime’…” Waitress:“Yeah.” “I’ll have the pancakes in the Age of Enlightenment.” <later, after complaining that his humor is lost on the waitress> “Miss, can we have the check…?” “Hang on, Voltaire.”
Sorry. It’s got to be “Juicyfruit.”
Wait Until Dark–That jump scene.
Reds–When Diane Keaton is in the train station, she opens her eyes and sees Warren Beatty and then slowly walks over to him.
I had to Google as well!
Lots and lots of great ones already gone but how about:
**The Italian Job **- “You were only supposed to blow the bloody doors off”
In the Heat of the Night - “They call me MR Tibbs”
The Caine Mutiny - Bogart with the ball bearings during the Court Martial
Or, *on *the River Kwai …
City Lights, when the flower girl recognizes the tramp.
Blazing Saddles "You want some beans, Mr. Taggart?
Awww … don’t kwai.
Inigo Montoya, “Begin.”
*Treasure of the Sierra Madre *has the original ‘stinkin’ badges’ scene, but to my mind, it’s one of the final scenes of the film that is perhaps the greatest in all of cinema: when Howard and Curtin realize that the gold has just blown away back into the desert, and all the agony has been for absolutely nothing, and they ultimately howl with insane, gut-busting laughter.
They just don’t make 'em like that anymore.
That moment from ‘To kill a mockingbird’ gets my vote too.
Saving Private Ryan: Opening scene.
Who Framed Roger Rabbit?: Opening scene.
One Flew Over The Cuckoo’s Nest; “But I tried, didn’t I, goddamit? At least I did that.”
Superman II: Clark Kent goes back to the diner truck where the big guy beat him the first time. “Pushups”.
Bringing Up Baby: “I was born on the side of a hill. I was born on the side of a hill.”
Psycho: Countless great scenes but I’ll mention just two self-contained masterpieces of scripting, acting and direction. (i) The traffic cop gets suspicious and questions Marion Crane. (ii) Arbogast’s quizzing of Norman Bates.
The Exorcist: Karras’s first ‘interview’ with the demon. “That would be far too vulgar a display of power.”
Love Actually: Mark stands on Juliet’s doorstep and tells her how he feels about her, without a single spoken word. Then says, as he walks away, “Let it go.”
The Sound Of Music: Maria’s outspoken protest to the Captain after she and the children have all fallen into the water and struggled ashore. “I am not finished yet!”
**Finding Nemo: **“No-one’s ever put up with me this long before.”
What’s Up Doc: Judy’s superb putdown. "Propriety; noun: conformity to established standards of behavior or manner, suitability, rightness, or justice. See “etiquette.” "
Beverly Hills Cop: Axel’s dismay at his colleagues. “Before I go, I just want you two to know something, alright? The supercop story… was working. Okay? It was working, and you guys just messed it up.”
Terminator 2: The T-1000’s bike leap from the burning building into the helicopter, with super eye candy special FX as he ‘pours himself in’ through the window. One suspects that creating this one sequence called for a great many people to put in a lot of hard work.
Slumdog Millionnaire: Jamal tracking down Latika at the train station.
The Railway Children: Bobbie looks through the steam and smoke on the railway platform and sees her father.
Paris, Texas: Travis’s final conversation with Jane.
To Have And To Have Not: “This bottle belongs to me and so do my lips.”
Mary Poppins: ‘Spoonful of Sugar’. Pure cinematic magic with FX that stand up well, even today.
Oliver: Pretty much all of it, but ‘You’ve Got To Pick A Pocket Or Two’ and ‘I’d Do Anything’ being special favourites.
Four Weddings And A Funeral: Matthew’s speech at Gareth’s funeral. “…duck a la banana”.
A Night At The Opera: The over-crowded state room.
American Gigolo: Final words, final scene: “I’ve waited so long for you.”
Life Of Brian: “We are all individuals!”
The Empire Strikes Back: Battle scene with the AT-ATs.
Goldeneye: The tank chase through St. Petersburg.
The Day The Earth Stood Still (1951): First appearance of Gort, and his ‘exchange’ with the military.
The Incredible Shrinking Man: Fighting the tarantula.
Shaun of the Dead: The leap over the fence.
Pulp Fiction: “I dare you to say ‘what’ again!”
Scrooge (1951): The morning following Scrooge’s change of heart, especially his teasing dialogue with Bob Cratchit.
Goodfellas: The famed one-take sequence into the nightclub.
Carousel: Dance sequence, ‘June Is Bustin’ Out All Over’
Onegin: “It’s too late”.
First of all, does the OP mean “best” as in “favorites” or as in “iconic”?
Second of all, Point Break is an adreneline filled thrill ride and a half.
Finally, I would also ad Keanu firing his gun in the air and yelling AAAAAAAAH! as an all-time iconic Hollywood scene.
Swingers - The always double down on eleven scene.
The birth scene in Children of Men, when they hear the baby cry and everyone just stops, the whole battle pauses to watch them walk through safely. And just as quickly as it stopped, BAM, it’s back on, blood and bullet everywhere. I’m not one to cry at movies, but that scene put a little dust in my eyes.