A few of my favorites:
Martin Luther King, Jr.
(1) We shall have to repent in this generation, not so much for the evil deeds of the wicked people, but for the appalling silence of the good people.
(2) The ultimate measure of a man is not where he stands in moments of comfort and convenience, but where he stands at times of challenge and controversy.
(1) It is not the critic that counts; not the man who points out how the strong man stumbles or the doer of deeds could have them 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 short again and again, because there is no effort without error and shortcoming; but he who does actually strive to do the deed; who knows the great devotion; who spends himself in a worthy cause, who at the best, knows in the end the triumph of high achievement, and who at the worst, if he fails while daring greatly, knows that his place shall never be with those cold and timid souls, who know neither victory nor defeat.
(2) Far better it is to dare mighty things, to win glorious triumphs, even though checkered by failure, than to take rank with those poor spirits who neither enjoy much nor suffer much, because they live in the gray twilight that knows not victory nor defeat.
(3) Don't hit at all if it is honorably possible to avoid hitting; but never hit softly.
(1) When the choice is between cowardice and violence, I would strongly recommend violence.