From the site Positive Atheism and WikiQuote:
The question before the human race is, whether the God of nature shall govern the world by his own laws, or whether priests and kings shall rule it by fictitious miracles?
-- John Adams, letter to Thomas Jefferson, June 20, 1815
The United States of America have exhibited, perhaps, the first example of governments erected on the simple principles of nature; and if men are now sufficiently enlightened to disabuse themselves of artifice, imposture, hypocrisy, and superstition, they will consider this event as an era in their history. Although the detail of the formation of the American governments is at present little known or regarded either in Europe or in America, it may hereafter become an object of curiosity. It will never be pretended that any persons employed in that service had interviews with the gods, or were in any degree under the influence of Heaven, more than those at work upon ships or houses, or laboring in merchandise or agriculture; it will forever be acknowledged that these governments were contrived merely by the use of reason and the senses.
-- John Adams, "A Defence of the Constitutions of Government of the United States of America" (1787-88), from Adrienne Koch, ed, The American Enlightenment: The Shaping of the American Experiment and a Free Society (1965) p. 258, quoted from Ed and Michael Buckner, "Quotations that Support the Separation of State and Church"
Facts are stubborn things; and whatever may be our wishes, our inclinations, or the dictates of our passion, they cannot alter the state of facts and evidence.
--John Adams, Argument in Defense of the British Soldiers in the Boston Massacre Trials (4 December 1770).
If they are good workmen, they may be of Asia, Africa, or Europe. They may be Mohometans, Jews or Christians of any Sect, or they may be Atheists.
-- George Washington, letter to Tench Tilghman asking him to secure a carpenter and a bricklayer for his Mount Vernon estate, March 24, 1784, in Paul F Boller, George Washington & Religion (1963) p. 118, quoted from Ed and Michael Buckner, "Quotations that Support the Separation of State and Church"
I am persuaded, you will permit me to observe that the path of true piety is so plain as to require but little political direction. To this consideration we ought to ascribe the absence of any regulation, respecting religion, from the Magna-Charta of our country.
-- George Washington, responding to a group of clergymen who complained that the Constitution lacked mention of Jesus Christ, in 1789, Papers, Presidential Series, 4:274, the "Magna-Charta" here refers to the proposed United States Constitution