At this point (a week before wide-release) talking about recasting is pretty disrespectful. At least wait to see the guys performance before you poop out boring, obvious choices of actors to play the role. You never know, if the hype is the real deal, someones going to have to have serious chops to follow what Ledger did.
A great example of this is The Crow. No one ever came that close to Brandon Lee's take on the character, everyone who followed seemed to Parody what he did. I know 75% of that was in the bad writing the actors had to work with, but the actors (some we're kinda talented) really just ended up mimicking Brandon even though they played different characters.