My personal favorite is Lincoln. A man didn't wait for someone else to do for him, but did it himself. As President he made tough decisions in the interest of the Republic not mob rule, he wasn't interested in public opinion polls.
However I think each Period in American History has it greats.
1)Thomas Jefferson- A man who thought, his ideas along with the the ideas of his adversary and friend, John Adams, helped form the basis of this free republic.
2)Teddy Roosevelt- A ahead of his time, he welcomed Booker T. WAshington into the White House as a guest when this was an uncouth thing to do. A man who realized, like it or not, America has a big role to play in international affairs.
3) Harry Truman- Willing to do what he had to do, definately not a push over
4) Gerald Ford- A peacable, likeable and honorable man.
5) Ronald Reagan- A modern day Thomas Jefferson in thoughts of liberty and personal reliance. Though their ideas of military would have clashed.