Airplane!, being the funniest thing ever, has quite a few. The most famous one is:
Ted Striker: Surely you can't be serious!
Rumack: I am serious...and don't call me Shirley.
Most likely due to its Hilarious in Hindsight implications, but this line coming from an elderly woman just overcome with airsickness, considering the person they were mocking didn't become president until a full year after the movie had been released:
Old Woman: I haven't been this sick since I saw that Ronald Reagan movie.
When Barbara Billingsly passed away, almost every online news source and blogger posted her "I speak Jive" clip. Definitely a Crowning Moment.
Any mention of Ted's "drinking problem".
Or his mind-numbingly boring stories of life after the army. Or rather, the reactions to said stories.
"It was a rough place - the seediest dive on the wharf. Populated with every reject and cutthroat from Bombay to Calcutta. It's worse than Detroit."
"Looks like I picked the wrong day to quit sniffing glue." *sniff*
Just about everything Stephen Stucker, as air control employee Johnny, said or did (bonus points to Stucker as these were all made up by him):
"Johnny, what do you make of this?" *hands him a computer printout*
"This? Why, I can make a hat, or a brooch, or a pterodactyl..."
"And Leon's getting laaaaaarger!"
"The tower? Rapunzel! Rapunzel!"
(after he has plugged back in the runway lights, which have gone out in the middle of an emergency landing) "Just kidding!"
(to Mrs. Oveur) "Where did you get that dress, it's awful, and those shoes and that coat, jeeeeez!"
"Me John Big Tree".
"Your husband and the others are alive, but unconscious." "Just like Gerald Ford."
"First the earth cooled. And then the dinosaurs came but they got too big and fat so they died and turned to oil. Then the Arabs came and they were driving Mercedes Benz's. And Prince Charles started wearing all of Lady Di's clothes. I couldn't believe it"...
The opening credits where the fin of the airplane doubles for a shark fin, complete with appropriate music!
"The hell I don't! LISTEN, KID! I've been hearing that crap ever since I was at UCLA. I'm out there busting my buns every night. Tell your old man to drag Walton and Lanier up and down the court for 48 minutes." (the look on Joey's face is priceless!)
"I just want to tell you both good luck. We're all counting on you."
"No, the white phone."
Otto the Autopilot. The look on his face when Elaine has to re-inflate him? Priceless.
And the bit where the doctor walks in, sees her inflating him, and turns around and walks straight out...
Ted buying a ticket for the plane and taking the smoking option. He's then handed a ticket that is literally smoking.
"Two more minutes?! They could be miles off course!" "That's impossible, they're on instruments!" And then we see that, yes, indeed they are....
The scene where the boy is reading a "Nun's Life" magazine, a few seats from the nun reading a "Boy's Life".
The scene where Ted and Elaine kiss on the beach. And then the waves come in and drench them. When they recede, Ted and Elaine are covered in seaweed and there's even some fish flopping about next to them.
Kramer: "I want every light you can get poured onto that field!" McCroskey (pointing out to the airfield): "Being done right now." Cut to a dump truck unloading electric lamps onto the ground.
Dr. Rumak's introduction. He is asked if he is a doctor. He replies yes...and for some odd reason he's wearing a stethoscope.