8. Harley Quinn
Though she was originally pencilled for inclusion in the ultimately doomed Batman Triumphant as Joker's daughter and not in her traditional role as lover and henchwoman, and rumoured to have been up for inclusion in The Dark Knight Rises (with Madonna and Kristen Bell attached to the respective roles), we are yet to see Harley Quinn on film, despite her being one of the most colourful characters in the Batman universe. That should change. Yes she's abrasive and annoying - or at least traditional screen versions of her, including in the Arkham games have been - but the reinvention of The Joker and Two Face in the last two films, as well as the intelligent take on The Scarecrow proved that there is scope to reimagine characters who have previously appeared in very different forms. Her inclusion would seem a reasonable answer to the question of how to give the Joker enough of an added dimension for a reappearance, and it would be good to include some female balance to the film after the success of both Selina Kyle and (to a lesser extent) Talia Al Ghul in The Dark Knight Rises.