I think Michael Goldfarb
very adequately spells out the case for disappointed Hillary Clinton supporters to join him in lining up behind John McCain -- if what you liked about Clinton was her support for the Iraq War and the Kyl-Lieberman resolution, McCain may be your man.
But if, like most Clinton supporters I'm aware of, you liked her work on expanding access to health care and building a more generally equitable United States of America, then it seems to me you're going to want to vote for Obama.
This article available online at:
http://www.theatlantic.com/politics/archive/2008/06/the-case/45297/