It's important to note though how meaningless national polls will be in this election. In this hyper-partisan age, most of the country is already decided leaving a very small 8-10% group of undecided voters that determine who wins the popular vote. That all but ensures a race that will be within 5%, which is the margin of error in most polls. Also ignore composite battleground state polls, they are also meaningless.
The numbers to watch are the individual battleground state polls, with the key states being Florida, Ohio, Pennsylvania, Virginia, Nevada, Colorado, Arizona, New Mexico, and New Hampshire. We haven't gotten too many updated state polls since Santorum exited the race, but we do have new numbers from Florida: