As for my TOP 20(in alphabetical order):
1."Ace Ventura: Pet Detective"
2."Bad Santa"
3."Better Off Dead"
4."The Big Lebowski"
5."The 'Burbs"
6."Christmas Vacation"
7."40 Year Old Virgin"
8."Four Rooms"
9."Get Shorty"
10."Ghostbusters"
11."The Hudsucker Proxy"
12."I'm Gonna Git You Sucka"
13."Mom & Dad Save the World"
14."The Naked Gun"
15."the Nutty Professor"(1996)
16."Old School"
17."Office Space"
18."Ruthless People"
19."Super Troopers"
20."What About Bob"

Thse movies had me laughing long after they were over. Just complete & utter goofiness!

It's a bit of a tough question to answer.. I love comedies but here's a list of my all time favorites:
The Big Lebowski- Steve Buschimi (can't be sure how to spell his name) is absolutely hilarious..in anything!
Snatch
Lock, Stock, and Two Smoking Barrels
Dumb and Dumber
Wayne's World
Drop Dead Fred
Romy and Michelle's High School Reunion
Office Space
Ace Ventura
Caddyshack
Napoleon Dynamite
I got a little carried away, I was going to try and keep this list as short as possible..
And shamefully and unfortunately I haven't seen Monty Python and the Holy Grail..

i didnt like spinal tap...it was boring

I hate to admit it, but the film that made me laugh harder than anything else was 'Team America: World Police'. I wish I could say it was something really intellectual. I think a lot of people in the UK had a similar reaction. I just go on what makes me laugh. Blazing Saddles, Airplane, The Man with Two Brains, Borat etc...

There's a little known comic strip film called 'Mr Jolly Lives Next Door', which may be the funniest thing Rik Mayall and Adrain Edmonson ever did. It also features the talents of Peter Cook. It's only available on a boxset now, along with all the other comic strip films.

Life of Brian.

Then daylight.......................

borat just kills me

Some less obvious choices

"The tall blond man with one black shoe" (the French version, not the abortion made with Tom Hanks)

"Clockwise" with John Cleese

"A Fish Called Wanda," obviously

"La Cage aux Folles" in the original French

And I agree about Borat. I laughed so much it hurt.

I agree with a lot of the movie choices already stated, here are some of my favorites:
Dumb & Dumber
Office Space
The Emperor's New Groove
Bad Santa (this one is a personal fave)
Sideways
Borat
Old School
Finding Nemo
Wedding Crashers
Planes, Trains and Automobiles (I don't think I saw this one mentioned before, it is really, really funny!)
Christmas Vacation
The Naked Gun
One Flew Over the Cuckoo's Nest
The Waterboy
Elf!!

And probably a ton more that I forgot.

Monty Python & The Holy Grail, by far.

Humor's hard to choose 'top ten' type lists b/c I think everyone's taste in what's funny is so varied. Most folks piss themselves over THERE'S SOMETHING ABOUT MARY while I was mostly bored. WAITING FOR GUFFMAN is classic in my book., but, when the mood is right, I love DUMB & DUMBER, too.

My favorite comedies are all the Scary Movies 1,2,3,4. Also I liked American Pie. Along with American pie 2 and American Wedding. The other American pie movies like band camp are o.k. But nothing can beat the one and only American Pie.

Martian Leader.