Airplane, hands down.
Closely followed by Monty Python's Life of Brian.
Best comedy film ever?
Impossible to call, but Billy Wilder has a solid canon, and Some Like It Hot is up there among the best.
On the domestic front you would probably be looking at one of the Alec Guiness' Ealing comedies, maybe Kind Hearts and Coronets.
Young Frankenstein 
Old School.
Some like it hot is overrated. Plase don't get me started on Will'I act like a child, and dress in 70's clothes to be funny' Ferrel.
Young Frankenstein is a good one though
.Blazing Saddles too.
Both Ace Ventura's and Dumb & Dumber. Plus all the Monty Pythons.
Airplane! for me too.
Though Happy Gilmore is up there too. "Tappety-tappety-tap-tap-tap"
Dan
Zoolander. Okay, it's not the funniest ever, but it's probably the funniest of the last 10 years. Oh, Anchorman was pretty good as well.
eugoogly.
South Park.
Quote: Gavin @ June 29 2008, 12:42 AM BSTSouth Park.
That really was very good.
This is Spinal Tap
His Girl Friday
Some Like it Hot
for starters
Blazing Saddles
South Park
Police Academy 1
Naked Gun
The Ladykillers (original).
Some Like It Hot is not over-rated in the least. It's excellent!
Totally agree with Airplane.
Quote: JuliaC @ June 29 2008, 1:51 AM BSTSome Like It Hot is not over-rated in the least. It's excellent!
(Round of applause) They're talking through their rectal cavity. Blazing Saddles gallops in a close second. Life of Brian next me thinks. Now you can all thank me for putting you right