What are the top 5 comedic movies of all time

The debate for the best comedies is subjective and open to debate.  What is considered humorous can vary by region and evolves over time.  With that said, here are 5 popular comedies:
 - Dumb and Dumber
 - Anchorman
 - Monty Python and the Holy Grail
 - Airplane!
 - Planes, Trains and Automobiles