Note to mods: all these quotes are much shorter than the works from which they are extracted, and so fall under fair use. The quote from Gibbon is also long out of copyright.

General

I like maxims that don't encourage behavior modification.

- Calvin (and Hobbes)

The world isn't fair, Calvin.

I know Dad, but why isn't it ever unfair in my favour?

- Calvin and Calvin's Dad

In theory, there is no difference between theory and practice. But in practice, there is.

- Yogi Berra

I'm all in favor of keeping dangerous weapons out of the hands of fools. Let's start with typewriters.

- Frank Lloyd Wright

Some cause happiness wherever they go; others, whenever they go.
- Oscar Wilde

That's no lady, that's my wife!
- Marx (Groucho)

The NHS kindly allows me to buy my own Aricept because I'm too young to have Alzheimer's for free, a situation I'm OK with in a want-to-kick-a-politician-in-the-teeth kind of way.

- Terry Pratchett

The optimist proclaims that we live in the best of all possible worlds, and the pessimist fears this is true.

- James Branch Cabell

Life is pleasant. Death is peaceful. It's the transition that's troublesome.
- Isaac Asimov

Bigamy is having one wife too many. Monogamy is the same.
- Oscar Wilde

If I were two-faced, would I be wearing this one?

- Abraham Lincoln

Now I am become death, the destroyer of worlds.

- Robert J. Oppenheimer (1904-1967) (citing from the Bhagavad Gita, after witnessing the world's first nuclear explosion)

I spent 90 per cent of my money on women, drink and fast cars. The rest I wasted.

- George Best

I choose a block of marble and chop off whatever I don't need.
- Francois-Auguste Rodin when asked how he made statues

You can't be optimistic with a misty optic.
- Stephen Cole, Ten Little Aliens

Believing in magic is easy, the reaction of a cowardly mind to explain away any phenomenon that vexes the intellect. But finding magic in the realities of existence... seeking out some hidden truth to cling to from every painful experience we endure... that is never easy.
- The Doctor, Ten Little Aliens

I too have known this thing called love, this ruler of hearts, this soul of our soul; it has never earned me more than one kiss and twenty kicks on the arse.
- Voltaire, Candide

What's life? Life's easy. A quirk of matter. Nature's way of keeping meat fresh.
- The Doctor, The Doctor Dances

Everybody has got to die, but I've always believed an exception would be made in my case.
- William Saroyan

Philosophy and Religion

For centuries, theologians have been explaining the unknowable in terms of the-not-worth-knowing.

- Henry Louis Mencken

Reason is the greatest enemy that faith has.
- Martin Luther, Table Talk, 1569

Now, now my good man, this is no time for making enemies.

- Voltaire on his deathbed in response to a priest asking that he renounce Satan.

'You see,' said Candide to Martin, 'crime is sometimes punished; that blackguard of a Dutch owner got the fate he deserved.'-'Yes,' said Martin, 'but did the passengers on board have to perish too? God punished the thief, the devil drowned the rest.'

- Voltaire, Candide

Your Highness, I have no need of this hypothesis.
- Pierre Laplace on why his works on celestial mechanics make no mention of God.

Jesus is Coming? Don't Swallow That.
- Anon

No man ever believes that the Bible means what it says: He is always convinced that it says what he means.
- George Bernard Shaw

I contend that we are both atheists. I just believe in one fewer god than you do. When you understand why you dismiss all the other possible gods, you will understand why I dismiss yours.

- Stephen Roberts

That which can be asserted without evidence can be rejected without evidence.
- Christopher Hitchens

Evolution does not require the nonexistence of God, it merely allows for it. That alone is enough to evoke condemnation from
those who fear the nonexistence of God more than they fear God
Himself.
- Keith Doyle

But how shall we excuse the supine inattention of the Pagan and philosophic world to those evidences which were presented by the hand of Omnipotence, not to their reason, but to their senses? During the age of Christ, of his apostles, and of their first disciples, the doctrine which they preached was confirmed by innumerable prodigies. The lame walked, the blind saw, the sick were healed, the dead were raised, daemons were expelled, and the laws of Nature were frequently suspended for the benefit of the church. But the sages of Greece and Rome turned aside from the awful spectacle, and, pursuing the ordinary occupations of life and study, appeared unconscious of any alterations in the moral or physical government of the world. Under the reign of Tiberius, the whole earth, or at least a celebrated province of the Roman empire, was involved in a preternatural darkness of three hours. Even this miraculous event, which ought to have excited the wonder, the curiosity, and the devotion of mankind, passed without notice in an age of science and history. It happened during the lifetime of Seneca and the elder Pliny, who must have experienced the immediate effects, or received the earliest intelligence, of the prodigy. Each of these philosophers, in a laborious work, has recorded all the great phenomena of Nature, earthquakes, meteors, comets, and eclipses, which his indefatigable curiosity could collect. Both the one and the other have omitted to mention the greatest phenomenon to which the mortal eye has been witness since the creation of the globe. A distinct chapter of Pliny is designed for eclipses of an extraordinary nature and unusual duration; but he contents himself with describing the singular defect of light which followed the murder of Caesar, when, during the greatest part of a year, the orb of the sun appeared pale and without splendour. This season of obscurity, which cannot surely be compared with the preternatural darkness of the Passion, had been already celebrated by most of the poets and historians of that memorable age.
- Edward Gibbon, Decline and Fall of the Roman Empire, Chapter 15

Music

I'm still trying to write that love-song
Maybe it'll prove that we were right
Or it'll prove that I was wrong
- Marillion, Kayleigh

It's six o'clock in the tower blocks
Stalagmites of culture shock
And the trippers of the light fantastic, bow down, hoe-down
Spray their pheromones on - this perfume uniform
- Marillion, Heart of Lothian

I'm in two minds, both of them are out of it at the bar
- Marillion, Just for the Record

So if you want my address it's number one at the end of the bar
- Marillion, The Last Straw

I remember doing nothing on the night Sinatra died

And the night Jeff Buckley died

And the night Kurt Cobain died

And the night John Lennon died

I remember I stayed up to watch the news with everyone

And that was a lot of nights

And that was a lot of lives

Who lost the tickets to what they need

- Badly Drawn Boy, You Were Right

You are young and life is long and there is time to kill today

And then one day you find ten years have got behind you

No one told you when to run, you missed the starting gun

- Pink Floyd, Time

If you're scared of dying, you better not be scared to live

- Eels, Friendly Ghost

The whole of Do You Realize? by the Flaming Lips forms a sort of existential poem I love, but I can't quote the whole thing for copyright reasons, so you'll have to read it here.