My favorite inspirational quotes come from Theodore Roosevelt.
"Friends, I shall ask you to be as quiet as possible. I don't know whether you fully understand that I have just been shot; but it takes more than that to kill a Bull Moose." (No, seriously. He was shot in the chest (the speech in his glasses case slowed down the bullet, but not enough for it to not penetrate his chest), and then gave a 90 minute speech.)
"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 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, who comes short again and again, because there is no effort without error and shortcoming; but who does actually strive to do the deeds; who knows great enthusiasms, the great devotions; 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, at least fails while daring greatly, so that his place shall never be with those cold and timid souls who neither know victory nor defeat."
But really, there are just so many great quotes out there.