From George Packer (2005), The Assassins' Gate: America in Iraq (New York: FSG: 0374299633) http://www.amazon.com/exec/obidos/asin/0374299633/braddelong00. Colin Powell's account of his last meeting with George W. Bush, as told by Colin Powell to George Packer:

In the same week of early January... Colin Powell was summoned to the White House for his farewell conversation with the president. All along, Powell had been the dutifully quiet dissenter on Iraq, concerned about the damage to alliances, skeptical (but not enough) of the administration's more fevered claims about weapons and terrorism, realistic about the difficulties of postwar. But his prestige was badly tarnished when his prewar speech to the UN about Iraqi weapons was proved mostly false. Though Iraq became more and more the responsibility of his agency, Powell had lost almost eery major fight back when the crucial decisions were made. His tenure as secretary of state was a great disappointment.... Now, sooner than he wanted, he was being replaced by Condoleezza Rice, a shrewder bureaucratic survivor.

After a few awkward minutes in the Oval Office, Powell realized that Bush had no idea what his secretary of state was doing there. The White House chief of staff, Andrew Card, was summoned, but he, too, was clueless. Who had called for the meeting? It began to seem entirely possible that the phantom vice president had arranged one more parting humiliation for his old colleague and more recent nemesis. Powell drew himself up and informed the president that he had come not for their weekly meeting but to say goodbye. Finding himself alone with Bush for perhaps the last time, Powell decided to speak his mind without constraint. The Defense Department had too much power in shaping foreign policy, he argued, and when Bush asked for an example, Powell offered not Rumsfeld, the secretary who had mastered him bureaucratically, not Wolfowitz, the point man on Iraq, but the department's number three official, Douglas Feith, whom Powell called a card-carrying member of the Likud Party. Warming to his talk, Powell moved on to negotiations with North Korea, and then homed in on Iraq. If, by April 1, the situation there had not improved significantly, the president would need a new strategy and new people to implement it. Bush looked taken aback: No one ever spoke this way in the Oval Office. But because it was the last time, Powell ignored every cue of displeasure and kept going until he said what he had to say, what he perhaps should have said long before.

At least, that's what Powell told Packer he said in his last meeting in the Oval Office. Is it accurate? I don't know: I do know that since his UN speech Powell's word trades at a very high discount indeed.