Some film buffs rate 'Young Frankenstein*' as Mel Brooks' best, but 'Blazing Saddles' is so funny, and so gleefully offensive to so many people, that it gets my vote. Cleavon Little and Gene Wilder's relationship is wonderful, but Harvey Korman really steals the show.
*"Fronk-en-shteen!"
And, if you love the movie, this documentary is very much worth 30 minutes of your time.