3. Ellen Page
Despite her short stature, Ellen Page has proved herself as one of the most forceful actresses working today. Her role in 2005's Hard Candy, as a young girl who turns the tables on a man she suspects of being a pedophile (Patrick Wilson), is a nightmarish vision of a young woman wise beyond her years- and someone who's arguably as mentally sick as her prisoner. Even before The Dark Knight came out, I had Page in mind for the role of Harley. Her performance as Haley in Hard Candy shows her ability to convincingly play a woman who has gone off the deep end but who still shows a great deal of humanity. Page's dry sense of humour in most of her roles, particularly since it usually has a sting to it, could also lend itself well to the role of Harley. While Page has already taken on a comic book role with Kitty Pryde in X-Men: The Last Stand and next year's X-Men: Days of Future Past, it'd be fun to see her play a super villain after playing a superhero.