9. Day of the Dead (1985)
Part three of what was once George Romero's zombie trilogy (he's made two more since), "Day" initially received tepid reception because it doesn't quite match the impact of the previous two movies ("Dawn" and "Night"). Nevertheless, time makes the heart grow fonder, and "Day" has stood up to be one of the genre's best films over the years. It is especially useful for one of the main characters' scientific examination of the zombies' physiology and psychology, providing more insight than any other film into what makes zombies tick.