The basis for the "16 words in the State of the Union Speech" was a set of forged documents called, collectively, the Niger forgeries. They were provided by the Italian Intelligence Service (SISMI) to both the U.S. and to the British. They were the alleged "proof" that Dick Cheney was told several times by the FBI Director, George Tenet, was not credible. Tenet had references to them removed from at least two speeches given by Cheney in the Fall of 2002.
In his Sunday "60 Minutes" interview Tenet says that the reference to Iraq seeking Uranium in Africa should have been removed from Bush's 2003 State of the Union speech, but that he did not himself read the speech before it was given and it slipped through. (This should be verified with whoever Tenet delegated the vetting of the speech to.)
Sen. Rockerfeller asked the FBI to thoroughly investigate the Niger forgeries years ago. And what has happened? Josh Marshall brings the story up to date.
Between Congressional the government oversight that the Democrats have reinstituted since regaining control of Congress, and the civil suit which Valerie Plame has filed (against Dick Cheney and a cast of characters from the White House), more will come out. Soon, I suspect.
Personally, I think that a key figure is going to be Michael Ledeen, a long-time radical Neoconservative who has strong right-wing connections in Italy and who was deeply involved in the Iran-Contra Affair during the Reagan administration.
So now we wait for the next shoe to drop.
As always, references to Wikipedia should not be considered authoritative. They provide good references.