"Always do right -- this will gratify some, and astonish the rest."
-- Mark Twain (1835-1910)
"The true measure of a man is how he treats someone who can do him absolutely no good."
-- Samuel Johnson (1709-1784)
"I've learned that people will forget what you said; people will forget what you did; but people will never forget how you made them feel."
-- Maya Angelou (1928-)
"Be nice to people on your way up because you meet them on your way down."
-- Jimmy Durante
(Source, for all of these: http://www.cs.virginia.edu/~robins/quotes.html)