Zombies, vampires, werewolves, mythological beasts and giants all fall into this category. The monster genre is so popular because it lets us explore the possibility of being something other than being human. Different monster films create different kinds of fear (i.e. the fear of turning into a monster or the fear of getting killed or eaten). 28 Days Later, Let the Right One In, Dracula and Godzilla are all great examples of monster movies.
Courtesy of consciouslyenlightened.com