1) Mitt is from a blue state and understands how to work with the other party: Mitt Romney spent four years as governor of Massachusetts, which is one of the bluest blue states. In fact, as Romney has noted many times, his legislature was 87% Democrats and yet, he still managed to pass legislation and balance the budget. On the other hand, Barack Obama has spent the last four years at loggerheads with the Republicans in Congress. You can argue about whose fault it is, but the fact of the matter is that Barack Obama and the Republicans in Congress have proven to be incapable of cooperating and that seems unlikely to change if he's re-elected. Maybe the same thing will happen if Romney gets into the White House, but he at least has a track record of success in that area while Barack Obama does not.
2) Mitt Romney is a moderate Republican: Take it from someone who ran Notmittromney.com during the primaries and preferred Newt Gingrich, Rick Perry, Herman Cain, Michele Bachmann, Rick Santorum, and Jon Huntsman to Romney: Romney was not one of the more conservative candidates running. Although it's possible that Romney will govern very conservatively if he's elected and many of us on the Right will do all we can to try to influence him to do that, the biggest reason some of us fought so hard to stop Mitt Romney was that we feared he would be just as much of a moderate in the White House as he was as the governor of Massachusetts. As a movement conservative, I consider that to be a bug, but if you're an undecided voter, that's probably exactly the kind of feature you're looking for in a President.