It was revealed on the McLaughlin Show that it was Karl Rove, the president's long-time advisor, who leaked Valerie Plame's name as a CIA agent whose portfolio involved stopping Weapons of Mass Destruction (WMD) from being proliferated. The speculation on DailyKos is that the investigator may have learned this quite some time ago and is seeking testimony from Matthew Cooper (Time Magazine) and Judith Miller (New York Times) that Rove and/or Bush committed perjury in his initial statement to the investigator. Lots of intriguing comments after both posts. A very interesting question in all this is: how did Rove get the name of a CIA agent in the first place? Atrios notes that if the story were untrue, then Rove has now had plenty of time to have disputed it.
UPDATE: I looked around for a summary of the Plame leak and found it inDKospedia. Don't mind the people trying to suggest that leaking her name wasn't a crime. The leak was treason.
Further update on Karl Rove: A few weeks back, Rove gave a speech on how liberals and conservatives respond to terror attacks. BTC News does a graph showing how Clinton's and Bush's terms compare in terms of casualties from terror attacks. It does NOT flatter conservatives!