I see a few good alternatives on some of the lists above (for my tastes). Mad, Mad, Mad, Mad World is a favorite though it gets perhaps a bit too crazy at times.
M*A*S*H was a good movie and very funny at parts, but I so enjoyed the TV series (which I saw many episodes of before seeing the movie of) that I never really enjoyed the movie.
The Pink Pather movies (with Peter Sellers) were funny though I like some of his other work a lot better. One of my favorite movies (period) is Being There, but another that he was in (The Mouse that Roared) is up there also.
Joe Dirt was ok for me, which is sort of funny since it was panned pretty badly by most people.
Wedding Crashers was ok but drug on a bit too long. For a second my dyslexia was kicking in and I was thinking the mention above was about The Wedding Singer which I also find funny.
My wife loved What About Bob, and I'm a big fan of National Lampoon Vacation. The original of that was pretty funny.
A movie I don't necessarily consider a comedy, but which isn't that much drama either, Silver Streak was very funny at times. It brought the great Gene Wilder and Richard Pryor pairing which was brought back for success later too.
My friends (at the site that inspired this article) mentioned Space Balls, which was also a favorite of my wife. That movie took many airings to grow on me. Much like another Mel Brooks classic, History of the World Pt. 1. I originally didn't appreciate either one that much, but after several watchings, I came to find them funnier.
Waynes World is another favorite, though I don't know it would be on my "all time favorites" list.
I'm also reminded of a few Jim Carrey titles: Liar Liar, The Mask, Me, Myself and Irene, and Bruce Almighty were pretty funny too. Anyway, several good choices up there though I'm interested in other alternatives still.