Libby's lawyers said in court that the "official" is someone "outside the White House." Novak said last year that President Bush knew the identity of his confidential source, and also suggested that the official also was Woodward's source as well.

Novak said in his July 14 article naming Valerie Plame that he had two Administration sources. One was later revealed to be Karl Rove. The other he has not revealed, although he has described him as "no partisan gunslinger" and as not working in the White House.

So, is it Stephen Hadley or Richard Armitage? Those are my best guesses.

Update: I've just finished reading the affidavit. Empty Wheel has some good analysis. I also tried removing the redactions and substituting names. While Armitage seemed the most likely, it occurs to me that particularly in this paragraph, Fitz might have not just used the source's last name, but included a "Mr." before it -- which would make a shorter name like Hadley still possible.

Another puzzle-solving paragraph is here. In this paragraph, it's unlikely Fitz would have included "Mr." since he didn't for Woodward, Novak or Libby, thus, again Armitage fits the best.

Tom Maguire's take is here.

Update: Another reason I'm going to go with Armitage is that Fitz in the affidavit and other pleadings has said he wants to keep the source secret so he doesn't become an "innocent accused." Hadley would not be described that way since he was a member of the White House Iraq Group. He may not have committed a crime, but he was in the thick of it. Armitage is far more likely to be a person Fitz would want to protect from being smeared.