Bride of Frankenstein(how do you justify added Son of Frankenstein) but not these two?)
King Of Kings(the 1927 silent version)
True Grit(the original)
(gulp)Birth of a Nation(it is extremely racist and offensive but everyone should watch it one time)
Judgement At Nuremberg
A Shot in the Dark
The Maltese Falcon
Raiders Of The Lost Ark
Angels With Dirty Faces
The Public Enemy
Planet of the Apes(the original)
"Son of Frankenstein" is a particular weakness of mine, as I think it's the absolute best of the Universal horror films. Completely subjective I admit.
The fun part of that particular list is that to add anything, you need to cut something. What would be removed to add four more Westerns? or Four more gangster films?
I think I had a list of 220 films to start with.
I love Duck Soup, maybe I'll solve the problem of two Casablancas by replacing "Night at Casablanca" with that.