Two questions: Leaving aside Florida, what blue states would Kerry be likely to lose? What red states would he be likely to win?
As for the the blue states, I'd say New Mexico would be the toughest to hold. Mainly because the Greens have a history of doing well in that state and a lot of voters there may be tempted to bolt over the war. Kerry's showing in Iowa gives him a decent shot to hold that state, and Wisconsin as well. Although the protest vote may also be a factor in Wisconsin. Other than that, I think Kerry can win every blue state.
As for the red states, clearly New Hampshire would be the most likely pickup. With someone like Edwards or Graham on the ticket, I think West Virginia is also a possiblity. Dukakis won that state, Bob Byrd is pissed and Gore had a lot of baggage from the eight years of the Clinton administration that hurt him.
Florida, Ohio and Nevada are other possibilities.