There are so many! Just a few for now... a small selection from some of my favourite people!

From the beautiful Kahlil Gibran...

• A shy failure is nobler than an immodest success.
• A fact is a truth unsexed.
• A madman is not less a musician than you or myself; only the instrument on which he plays is a little out of tune.
• Strange that you should pity the slow-footed and not the slow-minded, and the blind-eyed rather than the blind-hearted.
• You see but your shadow when you turn your back to the sun.
• A traveler am I and a navigator, and every day I discover a new region within
  my soul.
• A sense of humour is a sense of proportion.
• How mean am I when life gives me gold, I give you silver and I deem myself generous.
• Wisdom ceases to be wisdom when it becomes too proud to weep, too grave to laugh, and too self-ful to seek other than itself.
• A bigot is a stone-deaf orator.
• We often borrow from our tomorrows to pay our debts to our yesterdays.
  Half of what I say is meaningless; but I say it so that the other half may reach
  you.

In the words of Albert Einstein...

• Two things inspire me to awe - the starry heavens above and the moral universe within.
• Only two things are infinite, the universe and human stupidity, and I'm not sure about the former.
• The most incomprehensible thing about the universe is that it is comprehensible.
• A human being is part of a whole, called by us the "Universe," a part limited in time and space. He experiences himself, his thoughts and feelings, as something separated from the rest--a kind of optical delusion of his consciousness. This delusion is a kind of prison for us, restricting us to our personal desires and to affection for a few persons nearest us. Our task must be to free ourselves from this prison by widening our circles of compassion to embrace all living creatures and the whole of nature in its beauty.
• The important thing is not to stop questioning. Curiosity has its own reason for existing. One cannot help but be in awe when he contemplates the mysteries of eternity, of life, of the marvelous structure of reality. It is enough if one tries merely to comprehend a little of this mystery every day. Never lose a holy curiosity.

From books by Frank Herbert...

• What do you despise? By this are you truly known.
• You couldn't say something boundless within the boundaries of any language.
• How often it is that the angry man rages denial of what his inner self is telling him?
• Truth suffers from too much analysis.
• Power tends to isolate those who hold too much of it. Eventually, they lose touch with reality... and fall.
• Forget mystery and accept love. There's no mystery about love. It comes from life.
• We have forgotten that the word 'company' originally meant travelling companions.
• Do not be trapped by the need to achieve anything. This way, you achieve everything.
• Education is no substitute for intelligence. That elusive quality is defined only in part by puzzle-solving ability. It is in the creation of new puzzles reflecting what your senses report that you round out the definitions.
• Uproot your questions from their ground and the dangling roots will be seen. More questions!
• All definitions, no matter the language, should be considered probationary.
• Body jargon, hormone squirts, these begin to get at communication.
• Myths are not fiction, but history seen with a poet's eyes and recounted in a poet's terms.