It looks like Heath Ledger will play The Joker in a Batman Begins sequel.
Other actors which has been rumored to be in contention for the role include: Jude Law, Josh Lucas, Chrispin Glover, Jake Gyllenhaal, Paul Bettany, Steve Carell, Robin Williams and Lachy Hulme.
I think Ledger is more than competent to play the role, but is overall thought to be a weird choice. There are at least 4 actors on the list above that seem like more obvious choices. But may-be Christopher Nolan sees something we don't.
About the Sequel
The sequel will follow Batman as he enlists the aid of Gordon and Dent in "bringing down the Joker... but not killing him. In the third movie, the Joker would go on trial, scarring Dent in the process," says screenwriter David Goyer.
The rumored titles for the sequel include Batman Strikes, Batman Attacks, Batman Escalation, and Batman II. None of them sound good to me. Too bad Batman Returns was already used. Director Christopher Nolan is signed on and the sequel is commissioned for a 2008 release. Currently, Christian Bale, Michael Caine, and Gary Oldman are the only actors confirmed to reprise their roles for the sequel. Morgan Freeman has expressed interest in returning as Lucius Fox, but it is uncertain if his character will be needed in the second film.
About Heath Ledger
Heath Ledger blasted on to the scene in the 1999 teen comedy 10 Things I Hate About You. He went on to star in A Knight's Tale, Monster's Ball, The Order, Lords of Dogtown, The Brothers Grimm and Casanova. He was nominated for an Academy Award for his performance in Brokeback Mountain.