Christopher Nolan has written a tribute to Heath Ledger for newsweek. They also posted it on their website.. 

“One night, as I’m standing on LaSalle Street in Chicago, trying to line up a shot for “The Dark Knight,” a production assistant skateboards into my line of sight. Silently, I curse the moment that Heath first skated onto our set in full character makeup. I’d fretted about the reaction of Batman fans to a skateboarding Joker, but the actual result was a proliferation of skateboards among the younger crew members. If you’d asked those kids why they had chosen to bring their boards to work, they would have answered honestly that they didn’t know. That’s real charisma—as invisible and natural as gravity. That’s what Heath had…”

I suggest everyone go read the rest of this on the newsweek site..

“We cant quit you Heath!”