The Rand Corporation has established a tracking poll called the American Life Panel. They have been polling the same 3500 voters since July 5. They update their results every morning at 1:00 am. It's no shock that President Obama is leading in their poll. They have lots of "sub-polls," including intention to vote, predicted winner, and those changing their votes from one candidate to another. And each day, they have a different analysis based upon some other metric (today is was predicted winner based upon employment status of the voter). Other unique daily polls looked at voting by region, race, or economic status.
Today, the President leads by slightly more than 3 points (48.28 - 45). He has consistently led for nearly the entire time, save for a few days in July and the time surrounding the GOP convention. However, our President has lead by substantial margins on "predicted winner" since inception of the poll. His lowest margin was 10 points, and is currently at 13%.