“If chaos were lightning, then he’d be standing at the top of a hill in a thunderstorm, wearing copper armor and shouting, ‘All gods are bastards!’”
“I ask the court one key question, would the Space Corps ever have allowed this man to be in a position of authority where he might endanger the entire crew. A man so petty and small minded that he would while away the evening sewing name labels onto his ship issue condoms. A man of such awesome stupidity, he even objects to his own defence counsel, an over zealous trumped up little squirt…… an incompetent vending machine repair man with a Napoleon complex… who had as much respect from his crew-members as long John Silver’s parrot. Who would permit this man, this joke of a man, this man who could not outwit a used tee-bag, to be in a position where he might endanger the entire crew… who …. Only a yoghurt! This man is not guilty of manslaughter, he is only guilty of being Arnold J Rimmer. That is his crime, it is also his punishment!”
Next day it snowed, and killed off half the crops–but it was a good day.
It’s a cookbook!
Klaatu barada nikto.
You listening, Bog? Is a computer one of Your creatures?
So tomorrow we are heading up that Glory Road, rocks and all! Got any dragons you need killed?
“dn puǝ sıɥʇ.” -Sign at the End of the Universe by Duane Ackerson.
I love it. Infinity welcomes careful drivers.
“Smoke me a kipper; I’ll be back for breakfast.”
“What a guy!!”
[Here’s three from John Campbell. From this slashdot post. I’d heard the first and last before, but not the middle one.]:
“The basic rule of SF is: Set up a basic proposition–then develop its consistent, logical consequences.”
"No literature is sound, no philosophy of action workable, if it doesn’t take a hard look at itself. "
“Show me something that thinks as well as a man, but differently, and you’ve written a believable alien.”
In the beginning there was nothing, which exploded.
My favorite Terry Pratchett quote. 
I’ll be in my bunk.
Mostly harmless.
He shook his head in wonderment at the malevolent incompetence of the world.
Few people realize the immensity in which the dust of the universe swims.
“It wasn’t enough that humans did something so difficult as learning to play a musical instrument. Then they had to do it in groups. While walking around. In complicated patterns. And then they competed with one another to do it even better. Excellence, this kind of excellence, could never have any sane economic justification. It had to be done for the honor of one’s country, or one’s people, or the glory of God. For the joy of being human.”
Diplomatic Immunity by Lois McMaster Bujold
“Why does anyone want to go anywhere? Why did the bear go round the mountain? To see what he could see! I’ve never seen the Rings. That’s reason enough to go anywhere. The race has been doing it for all time. The dull ones stay home–and the bright ones stir around and try to see what trouble they can dig up. It’s the human pattern.” The Rolling Stones by Robert Heinlein.
The Princess looked at her more closely. “Tell me,” she resumed. “Are you of royal blood?”
“Better than that, ma’am,” said Dorothy. “I came from Kansas.” Ozma of Oz by L. Frank Baum.
“Open your eyes, and then open your eyes again.” The Wee Free Men by Terry Pratchett.
“Teach? No,” said Granny. “Ain’t got the patience for teaching. But I might let you learn.” Maskerade by Terry Pratchett.
“You must never run from anything immortal. It attracts their attention.” - Peter S. Beagle, The Last unicorn
“In his house at R’lyeh dead Cthulhu waits dreaming.” - Lovecraft
“Please put some flowers on Algeron’s grave.” - Daniel Keyes
The man gave a shrug which indicated that, although the world did indeed have many problems, this was one of them that was not his.
“This is Lord Mountjoy Quickfang Winterforth IV, the hottest dragon in the city. It could burn your head clean off.”
In fact, the mere act of opening the box will determine the state of the cat, although in this case there were three determinate states the cat could be in: these being Alive, Dead, and Bloody Furious.
“The very powerful and the very stupid have one thing in common - they don’t alter their views to fit the facts, they alter the facts to fit their views. Which can be uncomfortable if you happen to be one of the facts that needs altering.” ~The Doctor
Better yet “Ph’nglui mglw’nafh Cthulhu R’lyeh wgah’nagl fhtagn.”
(It’s probably better if you don’t read that one out loud. Just in case…)
Jane! Stop this crazy thing!
Thou art god… Valentine Michael Smith
OP, are you looking more for classic/famous quotes, or for witty ones?
Oh I like this one! Now when folks make cracks about my home I’ll have a comeback for them.