Ulysses31 named mine (honestly surprised it took that long). Monty Python's In Search of the Holy Grail is pure comedy at its best.
"How do you know she's a witch?"
"She turned me into a newt!"
"A newt?"
"Well...I got better."
For its cast alone, It's a Mad, Mad, Mad, Mad World deserves a huge nod. Where else can you see Buster Keaton, The Three Stooges, Jerry Lewis, Terry-Thomas, Sid Caesar, Uncle Milty, Jonathan Winters, Mickey Rooney...the list goes on and this is off the top of my head.
And, still, many scenes are quite memorable. Jonathan Winters' fight at the gas station. Dick Shawn ****** as he is going after his "momma". Spencer Tracy holding two phones together has his wife and soon-to-be-married ******** argue. Phil Silvers sinking in his car. And the fight on the ladder.
Dr. Strangelove, or How I Learned To Stop Worrying And Love The Bomb is another huge favorite. So many great one-liners.
"Shoot, a guy could have a good time in Vegas with this stuff."
"Gentlemen, you can't fight in here! This is the War Room!"
"Mein Furer! I can walk!"
There's Something About Mary cracks me up.