I nominate Patrick Bergin's illustrious lip sweater in Sleeping With The Enemy for Greatest Movie Mustache of all time.
I know, this seems like blasphemy, since Sleeping With The Enemy is such a god awful film. But that works in my reasoning. Of all the terrible things that go on in this putrid film (Julia Roberts' stiff acting, the horrible screenplay, Kevin Anderson's hilarious, almost date rape-y hairstyle), it is Bergin's picture-perfect face caterpillar that keeps you watching. I say this because I literally turned on the film on HBO, and watched it the entire way through just for that glorious mustache.
Any other movie mustaches that you would put above this one? I dare you to try. Warning: you will lose.