Doesn't have to be your most favorite, and I don't mind if it's song lyrics. I'll start with a few
"He who fights monsters should see to it that he himself does not become a monster. And if you gaze for long into an abyss, the abyss gazes also into you."
— Friedrich Nietzsche
"Every man has a point where he breaks or conjoins under pressures that flood to complicate." -Lyrics, Coheed and Cambria (Gravity's union)
"Let he who is without greed spark the first bowl."
- My roommate at about 3 in the morning.
Il semble que la perfection soit atteinte non quand il n'y a plus rien à ajouter, mais quand il n'y a plus rien à retrancher. - Antoine de Saint-Exupéry in Terre des Hommes, 1939
Faithful to the original French, (I've been told):
In anything at all, perfection is finally attained not when there is no longer anything to add, but when there is no longer anything to take away. - 1939 translation by Lewis Galantiere (Wind, Sand and Stars)
Bastardized version, familiar to most programmers:
A designer knows he has achieved perfection not when there is nothing left to add, but when there is nothing left to take away. - Eric S. Raymond (The New Hacker's Dictionary)