I don’t know why I’ve been on an IMHO kick lately.
I consider these five movies to be the most brilliantly and consistently witty that I’ve ever seen–and four of the five are just damn good films in and of themselves. Feel free to agree with me. 
If you haven’t seen these, rent two of them this weekend!
My choices:
These aren’t necessarily the BEST — deep social comment, inherent meaning, etc. But they are the funniest. They make me laugh. Overall, “Arsenic and Old Lace” is better than these – but I don’t laugh when I watch it.
Not even close.
Of course, funniest does not necessarily mean best. Woody Allen has done better films than “Love & Death,” but nothing funnier. Similarly, Chapin and Keaton made better films than those that I’ve listed, but they weren’t as laugh-out-loud funny.
Disagree… 
I like most of the ones you’ve named, but for just plain bust-a-gut funny? My top five in no particular order:
Blazing Saddles (“Are we awake?”/“We don’t know…are we…black?”/“Yes we are.”/“Then we’re awake. But we’re very confused.”)
It’s a Mad, Mad, Mad, (Mad?) World (esp. the new restored version with extra scenes)
What’s Up, Doc?
Ghostbusters (“The next time that someone asks you if you’re a God, YOU SAY ‘YES’!”)
The Court Jester (Danny Kaye, ca. 1955 or so)]
If I could go to seven, I’d add in a Marx Brothers film (maybe…arrgh…Freedonia…um…forgot the title) and "Return of the Pink Panther)
Fenris
In no particular order:
Airplane
Million-Dollar Legs
Horsefeathers
The Palm Beach Story
Sherlock, Jr.
The only one Gadarene mentioned that I’ve seen is * Groundhog Day, * which indeed is hilarious.
I go for:
*
No order.
These are all movies that I’ve laughed so hard at that I’ve cried.
Without a doubt;[list=1]
[li]Airplane![/li]
[li]The Producers[/li]
[li]Elephant Parts[/li]
[li]What’s Up Tiger Lily?[/li]
Any movie with Doroty Parker
Zentser—Umm, Dotty was never IN a movie. Except “Saboteur,” in which she had a cameo. And I’m afraid the scripts she contributed to were so watered-down that the movies themselves pretty much sucked.
BunnyGirl—I am very much afraid that if you and I ever had to decide on a movie to rent, bloodshed and tears would be the end result.
AIRPLANE!
All else pales by comparison…
All seemed funny at the time…
Airplane
Naked Gun
Bedazzled (original Peter Cook/Dudley Moore)
Holy Grail
Young Frankenstein
But most episodes of MST3K have more laughs per hour than any of the above.
The first ones that come to mind are:
Holy Grail
Young Frankenstein
Kentucky Fried Movie
It’s A Mad[sup]4[/sup] World
Blazing Saddles
Life of Brian
Clockwise
(Clockwise is a thing with John Cleese in it that had me laughing so hard I was crying.)
I know, that’s seven. I could probably think of many more.
Rosencrantz & Guildenstern Are Dead is one of my favorite films of all time, but not funny in a slapstick way.
Yeah, I’m probably defining “wall-to-wall funniest” in a different way than most people. My description of the films I listed as brilliantly and consistently witty is the standard by which I’m rendering judgment. (And by that standard, perhaps, Better Off Dead falls somewhat short…it’s more slapstick than the others.)
I tend not to actually bust a gut at anything other than Eddie Izzard, preferring instead dazzling, intelligent wordplay that makes me wish I’d said it first. The fact remains, though, that if you’ve ever found my sense of humor–as exhibited in my posts–at all appealing, I think you’ll really like the movies in the OP.
Three words… Shakes the Clown.
I can’t believe one of ya’ll has listed Animal House or Caddy Shack. Those were funny movies.
Yeah, they were. Both getting on my list.
Animal House
Caddy Shack
Ferris Beuller (I love this movie)
Ace Ventura (Jim Carrey at his best)
Naked Gun (They were all good)
No order.
The Jerk
Holy Grail
Caddyshack
Some Like it Hot
Young Frankenstein
Gee, for once I opened a movie thread before someone else posted all my favorites!
Some Like It Hot
Tootsie
Mad, Mad, etc. World
The Odd Couple
Raising Arizona
Planes Trains and Automobiles
The Meaning of Life
Animal House
Addams Family I & 2