Some quotes that I've heard or read somewhere and found interesting:

1. "Start at the beginning, proceed through the middle to the end, and then stop." - Alice's Adventures in Wonderland
2. "History doesn't repeat itself, but it does rhyme." - Mark Twain
3. "I believe one bad general to be worth two good ones." - Napoleon Bonapart
4. "A small mistake in the beginning leads to a big mistake in the end." - Thomas Aquinas
5. "If your boss demands loyalty, give him integrity.
   If your boss demands integrity, give him loyalty." - John Boyd
6. "Would you tell me, please, which way I ought to go from here?" (Alice)
   "That depends a good deal on where you want to get to," said the Cat.
   "I don't much care where..." said Alice.
   "Then it doesn't matter which way you go," said the Cat. - Alice's Adventures in Wonderland
7. "Less is more than more" - Adapted from the Gnu Less tool.
8. "He who controls the past, controls the future; and he who controls the present, controls the past." - George Orwell's novel 1984.
9. "The manager's function is not to make people work, it is to make it possible for people to work" - by Tom DeMarco and Timothy Lister in Peopleware: Productive Projects and Teams.
10. "Good decisions come from wisdom. Wisdom comes from experience. Experience comes from bad decisions." - Forbes magazine in 1987.
11. "...(software) is pure thought stuff, infinitely malleable." - by Fred Brooks in No Silver Bullet.
12. "The world is full of fascinating problems waiting to be solved." - by Eric Steven Raymond in How To Become A Hacker.
13. "Legacy code is code without tests." - by Michael Feathers in Working Effectively with Legacy Code.
14. "The large organization will consist of many semi-autonomous units (...) each of them will have a large amount of freedom, to give the greatest possible chance to creativity and entrepreneurship" - by Frederick P. Brooks in The Mythical Man-Month.
15. "If the problem being solved is unstated, it is unlikely that the solution will be either coherent or comprehensive." - by Richard Mortier and Emre Kiciman in Autonomic Network Management: Some Pragmatic Considerations
16. "A memory is what is left when something happens and does not completely unhappen." - by Edward DeBono
17. "If sharing a thing in no way diminishes it, it is not rightly owned if it is not shared." - by Saint Augustine
18. "Start small, think big, and keep yourself focused on your ultimate goal." - by Marie desJardins in How to Succeed in Graduate School: A Guide for Students and Advisors - Part 1 of 2
19. "The ultimate tragedy is not the oppression and cruelty by the bad people but the silence over that by the good people." - by Martin Luther King, Jr.
20. Being abstract is something profoundly different from being vague... The purpose of abstraction is not to be vague, but to create a new semantic level in which one can be absolutely precise." by Edsger Dijkstra in The Humble Programmer.
21. An architecture is simply the definition of the components of a system and their respective relations." by Pedro Sousa at IST
22. "And how do you know that you're mad?" (Alice)
    "To begin with, a dog's not mad. You grant that?" (Cheshire Cat)
    "I suppose so" (Alice)
    "Well, then you see, a dog growls when it's angry, and wags its tail when it's pleased. Now I growl when I'm pleased, and wag my tail when I'm angry. Therefore I'm mad." Alice's Adventures in Wonderland
23. "With or without religion, good people can behave well and bad people can do evil; but for good people to do evil---that takes religion." by Stephen Weinberg