The bias-cut, backless silk gown had fashion editors raving when it first appeared on screen last year.
It was voted top in a survey by Sky Movies and In Style magazine.
Marilyn Monroe's white dress from The Seven Year Itch, worn as she stood over a subway grate, was second.
The little black Givenchy dress worn by Audrey Hepburn in Breakfast at Tiffany's was third.
Olivia Newtown-John sported the first non-dress to appear at the list - her skin-tight black pants from the final scene of Grease came in at number four.
Coming in at number five was Kate Winslet's ensemble from Titanic.
The rest of the top 10 was:
6. Diane Keaton's tie and waistcoat in Annie Hall;
7. Nicole Kidman's satin corset from Moulin Rouge;
8. Liza Minnelli's stockings and bowler hat in Cabaret;
9. The gown worn by Cate Blanchett in Elizabeth: The Golden Age;
10. Vivien Leigh's dresses from Gone with the Wind.