TOD: Up to 1975, you say?
Peter Sellers
Marx Brothers
Carol Burnett and her crew on her TV show (though, I think you specified movies so that entry may not count)
Jack Lemmon in his comedies -- and he and Walter Matthau were always funny together
Mel Brooks' movies -- Young Frankenstein, The Producers
Madeline Kahn -- Blazing Saddles, Young Frankenstein
Monty Phython -- The Holy Grail (1975)
Babs in some of her comedies in the 60s like What's Up Doc? and The Owl and the Pussycat