Pineapple Express overall but a recent one that came out is Bad Neighbors with Seth Rogan and James Francos little brother and Zac Efron
SOME LIKE IT HOT (Marilyn Monroe's best flick IMO. She's so real and funny in it). Plus I totally like the Chicago gangster scenes (my hometown). And then we have Jack Lemmon and Tony Curtis in drag. It's a comedy way ahead of its time. QP TOOTSIE owes much to this original classic...
Planes, Trains and Automobiles still makes me laugh today. The orginal Arsenic and Old Lace is funny - Other runners up include Dumb and Dumber, The Naked Gun and Ace Ventura.
Some like it hot is a great film. I was a little skeptical before I first watched it but ended up loving it.
Pretty much anything from Monty Python, particullarly Holy Grail. Not very original, but it's the truth!