Batman Begins gave the whole franchise a new, more sinister tone, but it was The Dark Knight that packed a wallop and made us forget about its predecessors. (That means you, Batman & Robin.) Much of that is owed to the late Heath Ledger as the murderous Joker, reciting the chilling tag line "Why so serious?" with a Cheshire-cat-like grin. Superhero films have a reputation for being vapid, but The Dark Knight and Ledger's Oscar-winning performance proved otherwise.