One of the best has to be National lampoons christmas vacation, who can ever forget electrocuting the cat.
Though I am partial to the American pie movies, but they have overdone the franchise now.
It's a John Landis film with many a star in it (be it late 80's)
Remember seeing it round a mates house one Saturday night (ok i was a sad teenager)...we couldnt stop laughing...i laughed so much i was in pain, especially the first scenes with Arsenio Hall.
If you can pick up a copy, watch it, very funny indeed.
I don't think I've ever laughed as much at a film as I did at the end of The 40-Year-Old Virgin. But everybody else I know who saw it didn't think it was that funny!
Other favourites are:
Shallow Hal
Meet The Parents
This Is Spinal Tap
Elf
Happy gilmore
Army of darkness
Home alone
The man with 2 brains
Liar liar
Blazing saddles
and so on
I also recommend Amazon Women On The Moon, taped it of the telly a while ago. Truly funny film