This topic is close to my heart. I love comedy. I love to laugh, and I think that there is no such thing as a cheap or tasteless joke, as long as it makes someone laugh.
So what's your top 5 comedies and why? I'll start, in no particular order:
Arthur This might be my favorite film of all time. Non-stop laughs. Every character is hilarious and the writing is wow, ok. Even the sequel was pretty good, although not as brilliant as the first. Love that the 'lesson' from the film is that you can remain a drunk and still keep your fortune and get the girl
Dr Strangelove This really doesn't need an explanation.
The Graduate Some folks may not consider this a comedy, and I would agree that the second half of the film wasn't. But wow, the first half is just so awkwardly great.
The Producers (1969) Wonderful showbiz comedy. I love all of Mel Brooks stuff, but this, his first film, is still his best. I wish I knew how he managed to write his first (finished) feature script and convinced a producer to let him direct and have final cut. What?! How awesome would that be?!
A Fish Called Wanda We all knew that John Cleese was hilarious, but Kevin Kline? I was unawares until I saw this film. A wonderful zainy romp.
Some honorable mentions:
I Love You to Death
Some Like it Hot
Young Frankenstein
The Jerk
The Auteur
Bullworth
Good Morning Vietnam
Mrs Doubtfire
EDIT: Some more:
The Big Lebowski
Christopher Guest films
Noises Off
Goonies
What are yours?