First of all, I love Heath Ledger's Joker. But the reason why I pin this is because of the photos taken of his back. You can TELL he is The Joker from his back because Heath was full body acting. And it's beautiful to see.
EPIC : Heath Ledger as the Joker skate boarding over Christian Bale as Batman while they take a break on the set of The Dark Knight. You can all quit your lives now. Single greatest picture in the history of pictures and internet.