Off the top of my head:
From a while ago:
Quick Change
Swingers
Adaptation
Go!
Election
Get Shorty
Men in Black
More recent:
Zombieland
The Hangover
Enchanted
I have to add What About Bob? Also, Buckaroo Banzai.
The first movie I thought of was My Cousin Vinny.
Heck, the funniest movie I’ve ever seen is a silent film, for crying out loud. It was a film called Seven Chances, starring Buster Keaton. A man must marry by 7:00PM on his birthday or lose a huge inheritance from his grandfather. Trouble is it’s already his birthday!
If the plot sounds familiar it’s because it was remade in 1999 as The Bachelor, starring Chris O’Donnell. The Bachelor (1999) - IMDb This film was a dud compared to Keaton’s.
L.A. Story, 1991. Stars Steve Martin as a TV weatherman who finds love in L.A. with the help of a road conditions sign (which is a reincarnated set of bagpipes). That is actually one of the more coherent things about the movie.
Best In Show
Being John Malkovich
Waiting For Guffman
Offhand, I can’t think of any other truly funny movies from the past 15 years, and some of the more recent movies that seem to be generally considered hilarious (Wedding Crashers, The Hangover, Old School) are actually pretty dreadful, at least in my opinion.
Stepbrothers
Christmas Vacation
Ice Harvest
And some that were already mentioned.
Tropic Thunder
Dickie Roberts
Rat Race
South Park: Bigger, Longer, Uncut
Office Space
Liar, Liar
Pre-1990:
Airplane!
Naked Gun
Johnny Dangerously
All of Me
Raising Arizona
Young Frankenstein
Groundhog Day
Noises Off
Oscar
And pre-1990:
The Russians Are Coming, the Russians Are Coming
Better off Dead
One of the funniest of all time. Its so silly i love it.
Has anyone watched Klown streaming on Netflix? Very funny!
I’m just going to toss in my favourite pre-90’s as well. Here’s a jumbled mess of titles as I think of them.
The Life of Brian
A Fish Called Wanda (my all time #1 favourite)
Monty Python & The Holy Grail
Airplane (Really almost anything with Leslie Neilson in it)
The Hangover (#1 - the rerun #2 was much less so)
The Incredibles
Ghostbusters
Shaun of the Dead
Ace Ventura
Happy Gilmore (one of the few Adam Sandler pic’s that is really funny)
Beverley Hills Cop (Action comedy though depending if you want pure comedy)
Shaun of the Dead
40 Year Old Virgin (almost worth it for the waxing scene alone)
Knocked Up
The Princess Bride
Ferris Bueller’s Day Off
Caddyshack
Office Space
Hot Fuzz
Knocked Up
Pineapple Express
Forgetting Sarah Marshall
Planes Trains & Automobiles
Shrek
Coming to America
Dodgeball
Trading Americas
Burn After Reading
O Brother Where Art Thou?
The Big Lebowski
Pre-1990:
Raising Arizona
I’m sensing a pattern here…
Love A Fish Called Wanda
more recently… Tropic Thunder, Zombieland, Galaxy Quest
The Internet Movie Data Base is a better source of info. It’s from 1985.
Hmm, you know, most of my favorite comedies were pre-1990, and while I enjoy comedies, I couldn’t think of one I’d like to see right now. I generally enjoy my comedy mixed in with other elements such that it’s difficult to call it a comedy.
OK, skimming the thread, I have one: Oh Brother, Where Art Thou? Also, the MIB movies were fun.
My take on the Harold and Kumar franchise:
…White Castle was just stupid. Borderline un-watchable; also, a total letdown, since I generally love stoner comedies and White Castle.
…Guantanamo Bay is quite possibly one of the funnies movies I’ve ever seen. I went kicking-and-screaming to the video store to rent it, since HAKGTWC was such a dud, but it came highly recommended.
…3D Christmas I could take or leave.
The Big Lebowski
Napoleon Dynamite
Office Space
The Hangover
Groundhog Day
Zombieland
Harold & Kumar, Dumb & Dumber, Snatch ME TOO!
Shaun of the Dead is my favorite.
(just kidding) if **CalMeacham **and I are opposite sexes , **HeyHomie **is a ladyboy. 
you just can not dislike white castle while find Guantanamo Bay one of the funniest . (just my opinion)