Awesome marathon. Here are my suggestions. I don't know your tastes that well yet, so I'm kind of guessing based off what's already on the list.
Animal Crackers and A Night at the Opera. I see Duck Soup already on there. These two have equally funny gags, just not quite the lean mania found in Duck Soup, so they tend to be under-appreciated.
Grizzly Man and Fitzcarraldo. Didn't see any Herzog on the list. Have you seen either previously? I think you would like both.
The Hidden Fortress and Ran. Saw some Kurosawa and Star Wars on the list already. What continues to stick in my mind is the epic scope and spectacle of Ran. I find it really cool to see King Lear get a treatment like this. As for The Hidden Fortress, the sense of adventure and entertainment is the equal of anything Spielberg or Lucas has done in my mind.
Out of the Past. This is a dense noir with a terrific mystery. Kind of like The Big Sleep, but with the love story the focal point (like Double Indemnity) and Robert Mitchum instead of Bogey.
Ostrov. A recent Russian film about a man who becomes an Orthodox monk out of guilt. He has keen insight into the human heart, but can't forgive himself his past sin. The other monks misunderstand and mistrust him, as his holy fool antics and spiritual gifts make them feel embarrassed and inadequate.