In the first Austin Powers the scene after he was un-frozen where he did that huge wee made me laugh so much the first time I couldn't breathe.
Blazing Saddles I also found very funny indeed, althought it starts to get stupid towards the end.
Also Rat Race had some very funny moments in (the Claus Barbie musuem being one of them)
And then finally a little known film on the Vipco label called Drive in Massacre. Not supposed to be funny, but when me and a mate saw it we were rolling on the floor in laughter.