As well, Washington made very wise choices as president and put the best people in his administration, even though some of them were political enemies (e.g. Jefferson/Hamilton). Washington's conduct as president set the example for all presidents to follow and his gracious exit from the scene (when John Adams took the oath of office) set the stage for the continous string of peaceful transfers of power we enjoy to this day.
Lincoln is certainly second because he kept the Union together during a time when we could easily have turned into a place like Yugoslavia.
But as much as I like Reagan, I must place Nixon slightly ahead of him. Nixon got us out of the Vietnam War that the liberals bungled us into. Nixon reduced tensions with the Soviet Union, preventing any premature conflict and allowing Reagan to later finish the job (by letting the USSR bankrupt themselves trying to keep up with us militarily). Nixon opened the doors to China which was no small feat.
Sure, one can nitpick at Nixon's domestic policies. But remember that Nixon inherited the nation after Lyndon Johnson's disasterous "Great Society" was allowed to take hold. Like Reagan, Nixon was hamstrung by a Democrat controlled Congress. Nixon also had to face a genuine energy crisis and real economic problems that don't even compare to the ones we are dealing with today.
I liked Richard Nixon. His fault in Watergate was trying to coverup some silly election-year shenanigans and the liberals (who hated every cell in his body) roasted him for it. What Nixon's "plumbers" did in Watergate pales in comparison to the dirty deeds of the Clinton crime family. Nixon never framed innocent people so he could get them fired (Travelgate). Nixon never ripped off elderly people in a real-estate scam (Whitewater). Nixon never engaged in any sleazy "cattle trade" scams. Nixon never had his interns giving him oral sex in the Oval Office. Nixon never molested or sexually assaulted other women. Nixon didn't need a "bimbo eruption" squad. And when Nixon was about to get impeached, he resigned gracefully so as to spare the nation the experience. Unlike Clinton - who DID get impeached - Nixon didn't twist the arms of senators and bribe them in order to save his own political skin.
I can go on and on. But despite his obvious flaws, Richard Nixon was deep down inside a decent and honorable man and he served his country well.
Washington - Lincoln - Reagan. They're all indispensible men, in all honesty.