No kidding. Brief news with no details about cause of death here. The New York Post is calling it an apparent drug overdose, that "his apartment was strewn with sleeping pills and it was unclear if it was an intentional or accidental death." The New York Daily News also notes the presence of pills.
Channel 8 is running an eerie interview with David Moss where Ledger says that, because of his daughter's birth, "I feel good about dying now because I feel like I'm alive in her, you know. But at the same hand you don't want to die because you want to be around for the rest of her life."
Ledger was certainly an interesting actor, whether in an indie film like "Candy" or as one of the aspects of Bob Dylan in "I'm Not There." He had an Oscar nomination (for "Brokeback Mountain") and was part of a potentially huge commercial film, playing the Joker in the upcoming "The Dark Knight." (People.com has a timeline of Ledger's life and career here.)
His passing accordingly reminds me of the death of River Phoenix (although Phoenix was about five years younger than Ledger when he died). Some may recall James Dean dying young, too, but Dean achieved an iconic status that I don't think Ledger will have. Still, his resume to date suggested that he had a chance to be bigger than he already was, and that some great performances could have been waiting down the line.
You should also check out Daniel Fienberg's perspective, which is also about the celebrity-interview process.