4. Cassandra Cain
How there have been so many Batman movies without an appearance from Cassandra Cain is beyond me! Cassandra is the daughter of the assassins and key Batman characters David Cain and Lady Shiva and she left her father as a child after she killed a man. Soon after, after having saved Commissioner Gordon's life, she was adopted by Bruce Wayne who brought her up and trained her to later become the new Batgirl. Her skill and speed is even superior to Batman himself - she has developed almost superhuman speed, despite having no superhuman abilities, enabling her to dodge bullets easily. This version of Batgirl has an awesome costume - one that fanboys would go wild for in live action form - and she'd be a fantastic addition to any Batman movie franchise thanks to her fantastic martial arts skills and interesting back-story.