In the latest FiveThirtyEight post, Nate Silver makes the case for an 81% chance for an Obama win:

•  In some states, also, Mr. Obama is at 50 percent of the vote in the polling average, or close to it, meaning that he wouldn’t need very many undecided voters to win.
•  Mr. Obama is leading in the polls of Ohio and other states that would suffice for him to win 270 electoral votes
• By breaking polls down into three periods of about 10 days each, there is not much evidence to suggest "momentum" toward Romney. Instead, the case that the polls have moved slightly toward Mr. Obama is stronger.
• In the swing states, in fact, Mr. Obama’s polls now look very close to where they were before the conventions and the debates
• Obama has been ahead in the vast majority of polls in Iowa, Michigan, Minnesota, New Mexico, Nevada, Ohio, Pennsylvania and Wisconsin. These states add up to more than 270 electoral votes.

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