There's a teaser trailer up for the Dark Knight at a new viral site for the movie, while there's no footage from the movie shown what you do get is a few voice overs including Batman and Alfred discussing the motives of someone as crazy as the Joker and then you're treated to what Heath Ledger sounds like as the Clown Prince.

I'm a fairly big Joker fan, all the way back from the good old Adam West days, and really think the best Joker ever was Mark Hamil so as with anything where someone already has an Ideal image of a character something new is always held with much skepticism. Well I was quite impressed with Ledger's voice, especially the laugh--it's an eerie mix of Cesar Romero from the Adam West Batman, Mark Hamil and Ledger's own twist. It's quite good. The speaking voice sounds more like Jack Nicol son.

IGN also has an image of the Joker that's hidden somewhere on the viral site so if you don't want any visual spoilers just click on the link to Whysoserious.com and not IGN.

Source IGN