Surprisingly, I’m the first to say Raiders of the Lost Ark.
Asps. Very dangerous. You go first.
The Bounty, Ed Wood, What About Bob?, Master and Commander–the far side of the world, Ladyhawke, Donnie Darko, Brokeback Mountain.
I don’t think you’re allowed to claim the film and then misquote it.
Rocky Horror (with the exception of a few lines of dialog that were always talked over, but with multiple sets of audience participation lines)
Buckaroo Bonzai (“Where are we going!” “PLANET TEN!” “When?” “REAL SOON!”)
All About Eve
Clue
The Wizard of Oz
Grease - Wamma Damma Damma
Breakfast Club (though I don’t have it on DVD; it just always seems to be on t.v.)
Gone with the Wind - sometimes I just watch the first half 
BBC’s Pride & Prejudice
Casablanca and Life of Brian
Ooops. I googled to get it right since I was unsure - must’ve picked a bum page.
I mostly wanted to quote the “Real Soon” but didn’t want to make such a small quote that it seemed lost.
Mea Culpa. Next time I’ll just take off to IMDB.
Raising Arizona
O Brother Where Art Thou
Drop Dead Gorgeous
too many to list really.
Just this morning I had reasong to say “It’s a fine line between clever and stupid, really” (This is Spinal Tap)
Those are ones whose lines seem to fit seamlessly into my daily conversation.
Movies I’ve seen so often I’d feel fairly confident attempting to recite them include but are not limited to: When Harry Met Sally, Cars, Pride and Prejudice(K. Knightley), Princess Bride, Say Anything, Singing in the Rain and Star Trek II: The Wrath of Khan.
I’m surprised I’m the first to say The Godfather (the first, the second two not so much, though there are scenes from each).
Another Lion in Winter devotee as well. (“What family doesn’t have it’s ups and downs.”)
I can only think of one: Princess Bride
I’ve always felt this would be an excellent bumper sticker.
Another throw away line for Sampiro:
In a world where carpenter’s get resurrected, anything is possible.
The Breakfast Club
Ferris Bueller’s Day Off
Star Wars
Fargo
O Brother Where Art Thou?
Fellowship of the Ring
The Big Lebowski
Monty Python’s The Meaning of Life
Unkindly, when we see an extremely large fellow entering any restaurant we happen to be in, we usually whisper, “Oh, no, it’s Mr. Creosote!”
When we hear a particularly good song on the radio, we say in a thick southern accent, “It was a pow’ful air.”
When a blowhard is spouting on the news about something, we say “Well, that’s like, just your opinion, man.”
Surreptitious snacking at 10 a.m. is always called “Second Breakfast” in as Scottish a burr as we can manage.
One of my favorites follows Eleanor’s taunting of Henry when he suggests divorcing her and having sons with Alice even though he’s aging. She asks (I’m paraphrasing) ‘what sort of milky eyed, ricket ridden, lame and dimwitted kids’ he thinks he’ll be able to father.
HENRY: Eleanor… it’s so sweet of you to care.
The Glenn Close/Patrick Stewart version matches the old one for acting, but I LOVE the hamming and snarling of la Hepburn in that role.
To the OP:
Coming to America is one of those movies that I have to watch whenever it comes on and can recite everything (including the “she’s your queeeeeeeeen to be…” song) like catechism. My favorite lines will always be “He got Gillligggggaaaaaan off the Island!” and the one I quote most often when frustrated with friends, “Fuck you! Fuck you! And fuck you! Who’s next?”
If I had DVDs of Wizard of Oz, Young Frankenstein, and Singin’ In the Rain, this would be my exact list. Since I only have those on VHS I can only watch them for four months out of the year. (I have a computer-with-DVD-capabilities, but no TV and VCR, during the school year.)
“The pellet with the poison’s in the vessel with the pestle. The chalice from the palace has the brew that is true!”
“Yes, master. You can snap me in and snap me out!”
“Are they married? Order flowers for the widows, get it?” “Got it!” “Good!”
Jesus…probably the most seen is *Island of Lost Souls * (1932):
“Mr. Parker, do you know what it means to feel like God?”
"The natives…they are restless tonight. "
“Are we not men?”
Within the past few months, I have fallen competely in love with *Withnail and I * (1986):
“We want the finest wines available to humanity. And we want them here, and we want them now!”
“Right, here’s the plan. First, we go in there and get wrecked, then we eat a pork pie, then we drop some Surmontil-50’s each. That way we’ll miss out on Monday and come up smiling Tuesday morning.”
“I have a heart condition. If you hit me, it’s murder…my wife is having a BABY!”
“I must say, that represents a level of hypocrisy in you that I’d previously suspected, but not noticed due to highly evasive skills.”
“A pair of quadruple whiskies and another pair of pints…”
Monty Python and the Holy Grail- “Listen, strange women lying in ponds distributing swords is no basis for a system of government! Supreme executive power is a mandate from the masses, not from some farsical aquatic ceremony!”
Dirty Rotten Scoundrels- “Why is the cork on the fork?” “To prevent him from hurting himself, and others.” poke OW!
Young Frankenstein- “Would the doctor care for a brandy before retiring?”
Monty Python’s Life of Brian- “I have a vewy gweat fwiend in Wome named Biggus Dickus.”
South Park- “Oh I’m sorry I’m sorry. Actually what I said was…clicks on megaphone HOW WOULD YOU LIKE TO SUCK MY BALLS, MR. GARRISON?”
That reminds me. I really, really need a megaphone. There are just too many situations where it would be useful. One day when I am retired and rich and people have to suck up to me to ensure staying in my will, I am going to have a megaphone and I am going to use it for everything.
clicks on megaphone “WOULD YOU PLEASE PASS THE POTATOES?”
I’ve seen Gone With the Wind so many times I’m noticing what all the extras are doing around the periphery of a scene and how they’re dressed.
Others have already mentioned some I can do, Grail, Bride, Pulp, Buckaroo.
But I’m first with Repo Man.
“Lights are growing dim…I know a life of crime led me to this sorry fate… but in the end, I blame society, Society made me what I am…”
“That’s bullshit, Duke. You’re a white suburban punk, just like me.”
“Yeah, but it still… hurts” coughs bloods…
“Hey man, you’re gonna be alright.”
coughs more blood and goes limp.
“Maybe not.”
I know some of these have been mentioned already but the topic of this thread is a subjective question so there’s no harm in mentioning them again. I have large chunks of the following movies committed to memory.
The Wizard of Oz (as has nearly every American below the age of 70)
**It’s a Wonderful Life ** (like The Wizard of the Oz, due to its frequent TV broadcasts)
The Producers (1968 version)
Young Frankenstein
Raiders of the Lost Ark
Empire Strikes Back (I know this better than Star Wars for some reason.)
Monty Python and the Holy Grail
Goodfellas
Pulp Fiction (I’m surprised about how much of this movie I know. Probably because it’s been on the cable movie channels so often.)
12 Monkeys
The Usual Suspects
And a few runners-up in my personal “Movie Most Committed to Memory” contest:
Fight Club
The Hustler
Casablanca
Lawrence of Arabia (At four hours, there’s really too much in this movie for me too completely memorize.)
Vertigo
It’s a Mad, Mad, Mad, Mad World