Electoral-Vote.com has a preview of the 2008 Electoral Map based on recent polling data. Hillary Clinton currently has the edge over Barack Obama in the contest against John McCain as she has a better chance of winning Florida and Ohio.
With Obama as the nominee, the electoral college at the moment is Obama 260 to McCain 254 with 24 ties. With Hillary Clinton as the nominee, it is Clinton 289 to McCain 239 with 10 ties. Thus for the moment, her argument that she is more electable is true. Her strength is that she wins Florida and Ohio although he offsets this by winning Michigan and Iowa, which she loses. Also, he puts Colorado and North Carolina in play. If Obama were to win Colorado and McCain were to win North Carolina, they would each have 269 electoral votes and the new House would choose the President.