I have some Twain quotes on religion in a small blog called "What Would Mark Twain Say". You can see the full thing on Secular Perspectives at http://secularhumanist.blogspot.com/2011/04/what-would-mark-twain-s...
Here are a few:
In religion and politics, people's beliefs and convictions are in almost every case gotten at second-hand, and without examination. -- Mark Twain (He felt that we were trained into racial bigotry etc.)
“One of the proofs of the immortality of the soul is that myriads have believed in it. They have also believed the world was flat.” -- Mark Twain, Notebook (1900)
Cherish those who seek the truth but beware of those who find it. (Voltaire)
If God created us in his own image, we have more than reciprocated. (Voltaire)
People demand freedom of speech as a compensation for the freedom of thought which they seldom use. (Kierkegaard)
Religion is regarded by the common people as true, by the wise as false, and by the rulers as useful. (Edward Gibbon)
"I am an atheist, swear to god!"
-Hawkeye Pierce (from M.A.S.H.)
One of the favorite things I ever heard on a TV show...
Here's one I like:
"Christianity: The belief that some invisible cosmic Jewish Zombie can make you live forever if you symbolically eat his flesh and telepathically tell him that you accept him as your master, so he can remove an evil force from your soul that is present in humanity because a rib-woman was convinced by a talking snake to eat from a magical tree."