The New Hacker's Dictionary

((lambda (x)
 (list x (list (quote quote) x)))
(quote
 (lambda (x)
 (list x (list (quote quote) x)))))

This one works in LISP or Scheme. It's relatively easy to write quines in other languages such as Postscript which readily handle programs as data; much harder (and thus more challenging!) in languages like C which do not. Here is a classic C quine for ASCII machines:

char*f="char*f=%c%s%c;main()
{printf(f,34,f,34,10);}%c";
main(){printf(f,34,f,34,10);}

For excruciatingly exact quinishness, remove the interior line breaks. Here is another elegant quine in ANSI C:

#define q(k)main(){return!puts(#k"\nq("#k")");}
q(#define q(k)main(){return!puts(#k"\nq("#k")");})

Some infamous Obfuscated C Contest entries have been quines that reproduced in exotic ways. There is an amusing quine Home Page.

quote chapter and verse // v.

[by analogy with the mainstream phrase] To cite a relevant excerpt from an appropriate bible. "I don't care if rn gets it wrong; 'Followup-To: poster' is explicitly permitted by RFC-1036. I'll quote chapter and verse if you don't believe me." See also legalese, language lawyer, RTFS (sense 2).

quotient // n.

See coefficient of X.