They scooped everyone on the casting of Brandon Routh in Superman Returns, and now Latino Review says The Joker has been cast in the Batman Begins sequel:
We were first to tell the world that Brandon Routh was going to be the new Superman. Now here we are at it again as we just got word from A VERY TRUSTED SOURCE that the offer last night was officially made to Heath Ledger to star as The Joker in the Batman Begins Sequel!
Stay tuned for a possible official announcement.
Source: Yurka