I don't know if DC/WB have any live-action superhero projects in the works that would feature Batgirl, but I suddenly realized who I'd cast: Summer Glau. It isn't simply automatic fanboy "Summer Glau for everything" reflex, either. Reflecting on her past work, I think she'd be great for Barbara Gordon. And, of course, I'd love to see her in the costume (okay, that might be fanboy, I'll admit).
Who would you cast in the roles of your favorite heroes?