In a commencement speech at Stanford University in 2005, Steve Jobs said:
Your time is limited, so don't waste it living someone else's life. Don't be trapped by dogma - which is living with the results of other people's thinking. Don't let the noise of others' opinions drown out your own inner voice. And most important, have the courage to follow your heart and intuition. They somehow already know what you truly want to become. Everything else is secondary.
Here is the full commencement speech on Youtube:
Here is a link to the transcript of the speech.
And here is a link to a beautiful eulogy held by his sister, Mona Simpson