Matthew Yglesias points out an article suggesting that John Kerry make a Clinton his running mate -- and not the junior Senator from New York, either, but that other famous Clinton. The one who's been unemployed since noon on January 20, 2001.
Now, you're thinking that the Constitution probably forbids such a thing, and you're probably right, as Matthew describes; one Amendment says that "No person shall be elected President twice", but then, another says that "No person ineligible to be President shall be Vice President", although this might actually refer to the age and "natural born citizen" stuff, as opposed to the stuff about eligibility for mere election.
But really, the idea's just dumb, anyway. If a Kerry/Clinton ticket were even legal (and Matthew is right that surely it wouldn't be a good idea to have a ticket whose very legality would be a major issue), what of it? If Kerry/Clinton were elected, and Kerry died and thus re-elevated Bill Clinton to the Presidency, he'd be an instant lame duck. This would do the Democratic Party no good at all, since they'd have an incumbent ineligible to run again and thus would have to immediately start searching for yet another nominee; and it seems to me that the repercussions of such a transition from VP to President would be worse the closer one gets to the next election. If President Kerry were to die in, say, March of 2008, and VP Clinton ascended the Presidency but couldn't run again, the country would be in the position of having no fewer than three different Presidents in a period of less than one year. (Kerry, then Clinton, then the 2008 winner upon the 2009 Inauguration.)
So, even if the Supreme Court were to decide that Clinton could be Vice President, I don't think it would be a good idea. Now, I do think that a case can be made for allowing former Presidents who have had two terms to run again after a certain period of time -- say, two or three full terms -- given that lifespans are getting longer all the time. But even if such an Amendment to the Constitution ever comes to pass, I'm certain the language would "grandfather" Bill Clinton out of eligibility.
Bill Clinton, like him or hate him, is a compelling figure, and an important voice in America today. But he won't be President again.