Gone With The Wind?
Casablanca?
Personally, it's hard for me to separate my favorite movies from what I'd consider to be a great movie. (well, some of the time. Doug and Bob McKenzie's Strange Brew is still a favorite, although obviously not a great movie.)
Besides, what makes a movie the "greatest movie"??
The plots are *usually* pretty thin... The first couple of star wars were great for the advances in special effects. But, there wasn't that intricate of a plot, nor were the actors particularly good.
I just glanced at a list of the films that received Oscars for best film... but I disagree (strongly) with a few of them, particularly "Titanic" - the special effects were great, but the story was pretty lame (girl is suicidal, boy saves girl, girl (at a very vulnerable time emotionally) falls in love with boy... even for love stories, it was pretty lame. BTW, if that (4 letter word for engaged female who has sex with a guy she just met) had just stayed on the lifeboat, Jack could have been the one saved by floating on the hunk of wood (whatever it was).