A lot of films that came to my mind have already been listed, such as "The Searchers," "Casablanca" "Patton" and, yes, "Groundhog Day."
"It Happened One Night" should be on the list, as perhaps one of the best of the screwball comedies and one of the few films to sweep the Oscars for best picture, best actor and best actress.
"Gone With The Wind" has to make the list. It was bad history, but it is the Hollywood epic of the first half of the 20th Century.
"The Outlaw Josey Wales" remains my favorite Clint Eastwood film.
"Shane" wasn't a perfect film, but it had a near perfect ending, with "Little Joe" calling out for Shane to return.
Speaking of a near perfect ending, no film has ever so consistently caused my eyes to mist up every time I watch it than has "Field of Dreams." Maybe you have to be a guy whose father is dead to appreciate the closing scene.
"Blazing Saddles" is a classic.