A few from Theodore Roosevelt, to start:
"It is not the critic who counts: not the man who points out how the strong man stumbles or where the doer of deeds could have done better. The credit belongs to the man who is actually in the arena, whose face is marred by dust and sweat and blood, who strives valiantly, who errs and comes up short again and again, because there is no effort without error or shortcoming, but who knows the great enthusiasms, the great devotions, who spends himself for a worthy cause; who, at the best, knows, in the end, the triumph of high achievement, and who, at the worst, if he fails, at least he fails while daring greatly, so that his place shall never be with those cold and timid souls who knew neither victory nor defeat." -
"Citizenship in a Republic" - Speech at the Sorbonne, Paris, April 23, 1910
Related, earlier quotes:
"...the man who really counts in the world is the doer, not the mere critic-the man who actually does the work, even if roughly and imperfectly, not the man who only talks or writes about how it ought to be done." (1891)
"Criticism is necessary and useful; it is often indispensable; but it can never take the place of action, or be even a poor substitute for it. The function of the mere critic is of very subordinate usefulness. It is the doer of deeds who actually counts in the battle for life, and not the man who looks on and says how the fight ought to be fought, without himself sharing the stress and the danger." (1894)
And a few on other topics...
"The one thing I want to leave my children is an honorable name. It is hard to fail, but it is worse never to have tried to succeed." - Chicago, IL, April 10, 1899
"Be practical as well as generous in your ideals. Keep your eyes on the stars, but remember to keep your feet on the ground." - The Groton School, Groton, MA, May 24, 1904
"Optimism is a good characteristic, but if carried to an excess, it becomes foolishness. We are prone to speak of the resources of this country as inexhaustible; this is not so." - 7th Annual Message to Congress, December 3, 1907
"There are good men and bad men of all nationalities, creeds and colors; and if this world of ours is ever to become what we hope some day it may become, it must be by the general recognition that the man's heart and soul, the man's worth and actions, determine his standing." - Letter, Oyster Bay, NY, September 1, 1903
"If a man does not have an ideal and try to live up to it, then he becomes a mean, base and sordid creature, no matter how successful." - Letter to his son Kermit, 1915
"There are two things that I want you to make up your minds to: 1st, that you are going to have a good time as long as you live - I have no use for the sour-faced man - and next, that you are going to do something worthwhile, that you are going to work hard and do the things you set out to do." - Talk to schoolchildren in Oyster Bay, Christmastime 1898
"I have a perfect horror of words that are not backed up by deeds." - Oyster Bay, NY, July 7, 1915
"The object of government is the welfare of the people."
"Conservation means development as much as it does protection. I recognize the right and duty of this generation to develop and use the natural resources of our land; but I do not recognize the right to waste them, or to rob, by wasteful use, the generations that come after us." - "The New Nationalism" speech, Osawatomie, Kansas, August 31, 1910