I'm gonna have to say 'the ladykillers' was just a great comedy. alec guinnes is just brilliant in it.
also got to mention 'dr. strangelove'. strangelove is just genius.
both films contain the amazing peter sellers.
Fun fact: "Arsenic and Old Lace", the stage play, orignally had Boris Karloff in the role of the gangster who was always mistaken for...Boris Karloff. For some reason the studio opted not to hire him for the film adaptation and the role went out to someone who bore him a passing resemblance but who as most assuredly no Boris Karloff.
When I think of Ginger Rogers her name is usually paired with Fred Astaire (and I love their movies together) but one of my favourite classic comedies is The Major and the Minor with Ray Milland. It was Billy Wilder's debut as a director and I think it was a great start for him.
I love the Laurel & Hardy classics. Id recommend Sons of the Desert or Way out West for newcomers. Other than that, I second Arsenic and Old Lace as well. Almost all of the Ealing Studio films with Alec Guiness (Passport to Pimlico, Ladykillers, The man in the white suit) are amazing. Abbot and Costello meet Frankenstein is another, more of a goofy comedy movie that is worth watching.
Some of the old Steve Martin comedies were hilarious: Dead Men Don't Wear Plaid, Roxanne, The Man with Two Brains (if you're feeling a bit open minded) :) but I think they're the wrong era, unless you cheat the first one into it.
Ok, not exactly the golden age of hollywood. I have to say the marx brothers, duck soup. "Oh, I see, then it was murder. Will you marry me? Did he leave you any money? Answer the second question first."
some like it hot,big daddy,men in black,superbad,hot fuzz,the waterboy,the hangover and Night at the musuem are poperly comedies I can watch over and over and enjoy thats all I can think of now but I like lots of comedy movies.