Laws that May have been Broken by the Plame Leak

John Dean outlined some of the laws applicable to the leaker:

The Espionage Act of 1917

The Reagan Administration effectively used the Espionage Act of 1917 to prosecute a leak - to the horror of the news media. It was a case that was instituted to make a point, and establish the law, and it did just that in spades.
In July 1984, Samuel Morrison - the grandson of the eminent naval historian with the same name - leaked three classified photos to Jane's Defense Weekly. The photos were of the Soviet Union's first nuclear-powered aircraft carrier, which had been taken by a U.S. spy satellite.
...The Espionage Act, though thrice amended since then, continues to criminalize leaks of classified information, regardless of the reason for the leak. Accordingly, the "two senior administration officials" who leaked the classified information of Mrs. Wilson's work at the CIA to Robert Novak (and, it seems, others) have committed a federal crime...

The Intelligence Identities and Protection Act

Another applicable criminal statute is the Intelligence Identities Act, enacted in 1982. The law has been employed in the past. For instance, a low-level CIA clerk was convicted for sharing the identify of CIA employees with her boyfriend, when she was stationed in Ghana. She pled guilty and received a two-year jail sentence. (Other have also been charged with violations, but have pleaded to unrelated counts of the indictment.)
The Act reaches outsiders who engage in "a pattern of activities" intended to reveal the identities of covert operatives (assuming such identities are not public information, which is virtually always the case).
But so far, there is no evidence that any journalist has engaged in such a pattern. Accepting Administration leaks - even repeatedly - should not count as a violation, for First Amendment reasons.
The Act primarily reaches insiders with classified intelligence, those privy to the identity of covert agents. It addresses two kinds of insiders.
First, there are those with direct access to the classified information about the "covert agents." who leak it. These insiders - including persons in the CIA - may serve up to ten years in jail for leaking this information.
Second, there are those who are authorized to have classified information and learn it, and then leak it. These insiders - including persons in, say, the White House or Defense Department - can be sentenced to up to five years in jail for such leaks.

In a subsequent article, Dean pointed out:

"even if the White House was not initially involved with the leak, it has exploited it. As a result, it may have opened itself to additional criminal charges under the federal conspiracy statute."

As the media concentrates on the two reporters, it is not widely understood that their testimony is no longer necessary:

The special prosecutor investigating whether any Bush administration official may have violated federal law by leaking the identity of CIA officer Valerie Plame to columnist Robert Novak recently informed a federal court that his investigation has been “for all practical purposes complete” since October 2004.