Two great new featurettes on The Dark Knight have turned at Comcast.net. You can see them both here (look under 'Video').
The first is a piece on shooting sequences in IMAX ultra-high definition for the film. That one contains a smidgen of new footage. The other is about the creation of the masks worn by the Joker's goons and is actually the more interesting of the two. It shows some of the thought processes behind how the Joker's mind works. In short: he's screwy.