The Strategic Board Blog has a great list of CEOs who are blogging.

Some interesting blogs:
 Matt Blumberg, CEO,  Return Path – blogging since May 10, 2004
 Bob Lutz, Vice Chairman,  General Motors Corporation – blogging since January 5, 2005
 Ross Mayfield, CEO,  Socialtext – blogging since October 14, 2002
 Greg Papadopoulos, CTO,  Sun Microsystems, blogging since February 7, 2005