There are just so many good ones. I'll start with some nice historical ones.
"True philosophy must start from the most immediate and comprehensive fact of consciousness: I am life that wants to live, in the midst of life that wants to live."
--Albert Schweitzer
"The church says the earth is flat, but I know that it is round, for I have seen its shadow on the moon, and I have more faith in a shadow than in the church"
--Magellan
"From what God gives you, take that which you need. The rest is needed by others."
--St. Augustine
"If the liberties of the American people are ever destroyed, they will fall by the hands of the clergy."
--General Marquis de Lafayette
Not to disparage pop culture, since there are some good ones there:
"Frank, do you know what a hero is? Ninety-nine times out of a hundred, he's somebody who's tired enough, and cold enough, and hungry enough not to give a damn. I don't give a damn."
--Hawkeye Pierce
"Fifteen hundred years ago everybody KNEW the Earth was the center of the universe. Five hundred years ago, everybody KNEW the Earth was flat, and fifteen minutes ago, you knew that humans were alone on this planet. Just imagine what you'll KNOW tomorrow."
--K
"What's true in our minds is true, whether some people know it or not."
--Chris Nielsen
"The next time some asshole says to you 'I have a right to my opinion' you say 'oh yeah, well I have a right to my opinion, and my opinion is you have no right to your opinion'."
--George Carlin
"The most depressing thing about tennis is that no matter how much I play, I'll never be as good as a wall. I played a wall once. They're relentless."
--Mitch Hedberg
And, though long, my second favorite quote of all time:
"We succeeded in taking that picture, and if you look at it, you see a dot. That's here. That's home. That's us. On it, everyone you ever heard of-- every human being who ever lived-- lived out their lives. The aggregate of all our joys and sufferings, thousands of confident religions, ideologies and economic doctrines, every hunter and forager, every hero and coward, every creator and destroyer of civilizations, every king and peasant, every young couple in love, every hopeful child, every mother and father, every inventor and explorer, every teacher of morals, every corrupt politician, every superstar, every supreme leader, every saint and sinner in the history of our species, lived there on a mote of dust, suspended in a sunbeam."
--Carl Sagan (spoken while he looked at a photograph Voyager took of the Earth as it was leaving the Solar System)
