I'm having a hard time figuring out why this (of all things) would leak from the White House prior to the President's announcement, but the AP Wire reports that Ben Bernanke is expected to be nominated to replace Alan Greenspan:
Bernanke is an excellent choice. It will be interesting to see how the Fed now implements his ideas about more transparency in the Fed's communications with financial markets. I am particularly pleased that someone with such a talent and insight for research will be at the head of the Fed's staff of professional economists. I suspect that plenty of his former students are already there.
WASHINGTON - President Bush on Monday selected Ben Bernanke, chairman of the president's Council of Economic Advisers, to replace Alan Greenspan as Fed chairman, according to an administration official.
The official spoke on condition of anonymity because the nomination had not yet been announced. Bush was to announce his choice at 1 p.m. EDT, said White House spokesman Scott McClellan.
As usual, Grep Ip provides useful commentary in the Wall Street Journal.
UPDATE: See a sampling of blogger reactions at the WSJ's Econoblog site.