Man! This is going to be tough.
THE BIG LEWBOWSKI is by far the greatest comedy of all time. All time.
The next 19, probably not in order:
Dr. Strangelove or How I Learned to Stop Worrying & Love the Bomb
Office Space
Anchorman: The Legend of Ron Burgandy
The Life Aquatic With Steve Zissou
Ferris Bueller's Day Off
Clerks (Have yet to see 2, it probably deserves a spot up here)
Coming to America
Fight Club
Raising Arizona
Chasing Amy
Old School
Trading Places
O Brother, Where Art Thou?
Beverly Hills Cop/BHC2(Nothing beats Rosewood in the trenchcoats with the shotguns)
Monty Python & The Holy Grail
Tommy Boy
The Gods Must be Crazy
Thank You For Smoking
SNAKES ON A PLANE
My list kicks ass, I know.