The national polls--with the exception of Gallup, which is undersampling minorities--are very close, but as always, it is the electoral college that matters. If Obama wins the states the Democrats have won in the last five elections (which seems likely) plus New Mexico (which is almost certain), he has 247 electoral votes. Throw in Ohio and he is at 265. From there, winning just one swing state bigger than New Hampshire is enough. Without Ohio, Romney has no chance. If Romney wins only his base plus Ohio, he's not home free yet, but if he wins Ohio, he is very likely to win North Carolina, Virginia, and Florida as well, and that would get him very close to 270. So in the last two weeks, there will be a lot of focus, energy, and money poured into Ohio.
http://electoral-vote.com/