This is one of my favorites:
"And so, my fellow Americans: ask not what your country can do for you. Ask what you can do for your country."A famous quote by John F. Kennedy (May 29, 1917 – November 22, 1963).
This one could go back farther, but I heard it all the time when I was a kid.
"In the End, we will remember not the words of our enemies, but the silence of our friends."Martin Luther King Jr. (1929-1968)
I like this.
“Live as if you were to die tomorrow. Learn as if you were to live forever.”Gandhi
"It has become appallingly obvious that our technology has exceeded our humanity."Albert Einstein
There are only two ways to live your life. One is as though nothing is a miracle. The other is as though everything is a miracle."Albert Einstein