I can think of but three that should be instantly recognizable. To wit:
“Stella”
“Rosebud”
“Plastics”
but I’m sure there are more.
No fair using the main character’s name à la “Superman?” nor plucking one word out of what is really an extended quote as in: “Greed….” or “Badges?..”
Then again, who cares.
What movies can be recognized by a quote consisting of a single word?
KKKKHHHHHAAAANNNNN
Khaaaaaaaaaan!!!
Aaaaaaaaaaaanniee!!!
Indians!
brfffffffrrt
(that’s a fart sound)
Blazing Saddles?
“Beuller?”
“Thirty-seven!”
Adrian!
No!!!
Her? (this one is a TV show)
Humbug
SUPERMAN!
(from The Iron Giant)
Um, I know about Citizen Kane, but where do the other two come from?
May I add a clearly recognisable ‘Supercalifragilisticexpialadocious’.
A Streetcar Named Desire and The Graduate.
A Streetcar Named Desire and The Graduate.
Waaaaayne!
“Hope.”
Q.E.D., you just can’t seem to catch a break in this thread, can you? 
OOOOOOKKKKKK-lahoma
Thanks, I haven’t seen Streetcar :o .
Is the full phrase from The Graduate “the future is … plastics”?
Here’s another one:
‘precioussss’
I think you all know that one!
“Shane!”