Blazing Saddles
Clue
“I had to stop her from screaming!”
Since Blazing Saddles and Airplane! are already taken…
I have to say Airplane! 
Two not seen so far:
Naked Gun (Police Squad first movie)
Ruthless People.
Dirty, Rotten Scoundrels
Oh bloody hell…just did a google search and Ruthless People is also a Abrahams, Zuxker and Zucker film (like The Naked Gun and Airplane!). I didn’t know that. I guess they just hit my funny bone.
The Big Lebowski
Monty Python and the Holy Grail
Second choice Duck Soup
Airplane!
Young Frankenstein
(What knockers!)
Airplane!
(gawd, I’m so original)
I have to say though…that I knew I was getting older when I would quote Blazing Saddles and the young ens out there didn’t know where it came from. Blazing Saddles was the most quoteable movie of my generation.
I still have to resist (and sometimes unsuccessfully) whenever I play Battleground Europe and someone asks me if I have a plan…
…well…I thought we’d go aridin inta town…a shootin and ahollerin…killin everything in sight.
Planes, Trains & Automobiles
“You’re fucked.”
Nice to see Clue on here, though. Excellent movie.
A Fish Called Wanda
“The London Underground is not a political movement!”
That’s stupid.
Office Space
Going old school:
Arsenic and Old Lace
I can’t possibly pick THE one, but since so many of my all-time faves have already been posted I want to add this to the list:
“What’s Up, Doc?”
(“Mister Pleasure, it’s a Larrabee to …”)
Airplane!
This Is Spinal Tap
Well most of my favorites have been said, so I will go with underrated comedy. The Party, with Peter Sellers.