Monty Python and the Holy Grail
I love this, even though it doesn't have any of my top Python songs - hilarious slapstick, start to finish, and the funniest opening credits sequence I've ever seen ("The people who fired those people have now been fired").
Best bits: The Black Knight, "Your mother was a hamster and your father smelt of elderberries" (did I butcher that?), The questions three, The knights who say "ni".
I got into Monty Python relatively late; I'm glad I did though.