Depends on what kind of funny.
Fletch, Groundhogs day and Tommy Boy if we're talking SNL alum movies.
If you like a cheap laugh then Airplane and Naked Gun are great
Blazing Saddles, Young Frankenstein and Holy Grail are the top of the list when it comes to satire.
Windy City Heat is a hysterical unknown film.
Kevin Smith pre Dogma also gets my vote.