Whodunit? Who leaked the name?
It was Richard Armitage, Colin Powell's deputy, in 2003.
Since then, Armitage himself, Colin Powell, and Patrick Fitzgerald have known it was Armitage, and no one stopped the silliness of the political witch-hunt Plame investigation.
I haven't followed this closely, but Tom Maguire has. Stroll on over there if you want all the theories and the motivations and the back-stabbing and the duplicity.