There are several lines that come to mind.
"Another world is not only possible, she's on her way. Many of us many not be around to greet her, but on a quiet day, if I listen carefully, I can hear her breathing."
- Arundhati Roy
"Be ashamed to die until you have won some victory for humanity."
- Horace Mann. This was extremely frequently repeated at the college I attended, so much so that we often just shortened it to "be ashamed."
And on a light note, Christopher Walken's lions speech from Poolhall Junkies:
"Don't beat him. Kick his ass."
http://www.youtube.com/watch?v=jzekDivpK3M