I started with just a few, but found too many to put in one post. These are among the many that resonated with my own beliefs:

“I do not consider it an insult, but rather a compliment to be called an agnostic. I do not pretend to know where many ignorant men are sure — that is all that agnosticism means.”

–Clarence Darrow

“I distrust those people who know so well what God wants them to do because I notice it always coincides with their own desires.”

–Susan B. Anthony

“The more I study religions the more I am convinced that man never worshipped anything but himself.”

–Sir Richard F. Burton

“My atheism, like that of Spinoza, is true piety towards the universe and denies only gods fashioned by men in their own image to be servants of their human interests.”

–George Santayana

“I do not feel obliged to believe that same God who endowed us with sense, reason, and intellect had intended for us to forgo their use.”

–Galileo Galilei

“To assert that the earth revolves around the sun is as erroneous as to claim that Jesus was not born of a virgin.”

–Cardinal Bellarmino, during the trial of Galileo;
he also said, “Freedom of belief is pernicious.
It is nothing but the freedom to be wrong.”

…and quite apropos to the current administration:

“A tyrant must put on the appearance of uncommon devotion to religion. Subjects are less apprehensive of illegal treatment from a ruler whom they consider godfearing and pious. On the other hand, they do less easily move against him, believing that he has the gods on his side.”

–Aristotle

Sources: here, here, here, and a lot more here.