I would have added:

1776

All Quiet on the Western Front(the original)

Patton

Godfather Part 2

Goodfellas

Empire Strikes Back

Return of the Jedi(you are on a Star Wars forum and you don't include the whole OT?!?! SHAME ON YOU!!!)

Both versions of Ben Hur

Frankenstein

Bride of Frankenstein(how do you justify added Son of Frankenstein) but not these two?)

King Of Kings(the 1927 silent version)

High Noon

Stagecoach(the original)

The Shootist

True Grit(the original)

The Searchers

(gulp)Birth of a Nation(it is extremely racist and offensive but everyone should watch it one time)

Schindler's List

Judgement At Nuremberg

A Shot in the Dark

The Maltese Falcon

Raiders Of The Lost Ark

The Hustler

Little Caesar

Angels With Dirty Faces

The Public Enemy

Duck Soup

Planet of the Apes(the original)