Ohio, or a mixed bag
I'm going to assume the states for Bush right now are pretty much going to stay that way, and the same for Kerry. Assuming Florida stays in Bush's column and Pennsylvania in Kerry's, Ohio is now the big cheese. If Bush wins Ohio, he wins the election. Without Ohio, assuming Bush gets Wisconsin he can them take any of Iowa, New Mexico, or ME/CD2 + New Hampshire to get to at least 269, where the House breaks a tie in Bush's favor.