The final Pew Poll before the 2012 election predicted an Obama 50% & Romney 47% outcome.
The actual election result was Obama: 51.1% & Romney 47.2%.
They were one of the most accurate polling organizations.
http://www.realclearpolitics.com/epolls/2012/president/us/general_election_romney_vs_obama-1171.html
And did the internals of each poll change as it got closer to the election, either D vs R vs I percentages, or adults / registered voters / likely voters?