In the latest issue of VANITY FAIR: "Woodward was in a tricky position. People close to him believe that he had learned about Plame from his friend Richard Armitage, Colin Powell's former deputy, who has been known to be critical of the administration and who has a blunt way of speaking. 'That Armitage is the likely source is a fair assumption,' former WASHINGTON POST editor Ben Bradlee said." 'I had heard about an e-mail that was sent that had a lot of unprintable language in it.'" Developing...

This makes eminent sense to me as Fitz has implied Woodward's source was an innocent who would not be charged, hence, his refusal to name him in pleadings in the Libby case. As I wrote here,

Another reason I'm going to go with Armitage is that Fitz in the affidavit (pdf) 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.

Michael Isikoff of Newsweek also has speculated on Armitage. A compilation of Armitage news articles on his role is here.

Update: The Washington Post reports on the Vanity Fair article and says:

In an interview yesterday, Bradlee said he does know the identity of Woodward's source and does not recall making that precise statement to a Vanity Fair reporter. He said he has no interest in unmasking the official who first told Woodward about Plame in June 2003.

"I don't think I said it," Bradlee said. "I know who his source is, and I don't want to get into it. . . . I have not told a soul who it is."