Way too many to pick just one.
Any of the Marx Brothers films up to Night at the Opera for good laughs
Lots of good Westerns. Fort Apache, Darling Clementine, Destry Rides Again, Ox Bow Incident is a great film too.
Casablanca, Maltese Falcon with Bogie. Sahara is a guilty pleasure with Bogie and the tank that never runs out of gas.
Battleground, Best Years of our Lives for WW2 era stuff. Air Force is my guilty pleasure WW2 aviation film with the B17C "Mary Ann' that wins WW2 by itself.
Philadelphia Story, It Happened One Night for the romantic comedy stuff.
The list goes on and on.