Friedrich Nietzsche.
"And those who were seen dancing were thought to be insane by those who could not hear the music"
"You have your way. I have my way. As for the right way, the correct way, the only way, it does not exist."
"Whoever fights monsters should see to it that in the process he does not become a monster, and if you gaze long enough into the abyss, the abyss will gaze back into you."
"He who has a why to live for can bear almost any how."
"There is always some madness in love, but there is also always some reason in madness."
I could recommend almost any Nietzsche but the third quote is perhaps my all-time favourite, from the first philosophy book I ever pulled off the shelf and attempted to read; "Beyond Good and Evil". Its a dense little book, the Maxims and Interludes are my favourite.
Albert Camus.
"In the depth of winter, I finally learned that within me there lay an invincible summer."
"Nobody realizes that some people expend tremendous energy merely to be normal"
"I leave Sisyphus at the bottom of the mountain. One always finds ones burden again, but Sisyphus teaches the higher fidelity that negates the gods and raises rocks. He too concludes that all is well. This universe henceforth without a master seems to him neither sterile nor futile. Each atom of that stone, each mineral flake of that night filled mountain, in itself, forms a world. The struggle itself towards the heights is enough to fill a mans heart. One must imagine Sisyphus happy."
"You will never be happy if you continue to search for what happiness consists of. You will never live if you are looking for the meaning of life."
"Fiction is the lie through which we tell the truth."
Be better than me, read "The Stranger"
Johann Wolfgang von Goethe.
"Daring ideas are like chessmen moved forward. They may be beaten, but they may start a winning game"
"Knowing is not enough; we must apply. Willing is not enough, we must do."
"If you've never eaten while crying you don't know what life tastes like"
"If you treat an individual as he is, he will remain how he is. But if you treat him as if he were what he ought to be and could be, he will become what he ought to be and could be"
"Whatever you can do or dream you can, begin it. Boldness has genius, power and magic in it."
Goethe is just cool, read his Wiki page because its fucking remarkable. Check out his poem "Prometheus" and book "The Theory of Colours"
Immanuel Kant.
"Act in such a way that you treat humanity, whether in your own person or in the person of any other, never merely as a means to an end, but always at the same time as an end themselves."
"Whereas the beautiful is limited, the sublime is limitless, so that in the presence of the sublime, attempting to imagine what it cannot, has pain in the failure but pleasure in contemplating the immensity of the attempt."
"All our knowledge begins with the senses, proceeds then to the understanding, and ends with reason. There is nothing higher than reason."
"But only he who, himself enlightened, is not afraid of shadows"
"Seek not the favour of the multitude; It is seldom got by honest and lawful means. but seek the testimony of few; and number not voices, but weigh them."
Read "The Critique of Pure Reason" perhaps the most important philosophical text of the past five hundred years, if not ever. It is as challenging a book as you'll find, often requiring an entire university course to sift through, use SEP (the Stanford Encyclopedia of Philosophy) as an aide, from a scholarly perspective it might be the most valuable peer-reviewed, citable website on the internet.
Fyodor Dostoyevsky.
"Above all, don't lie to yourself. The man who lies to himself and listens to his own lie comes to a point that he cannot distinguish the truth within him, or around him, and so loses all respect for himself and for others, and having no respect he ceases to love"
"Pain and suffering are always inevitable for a large intelligence and a deep heart. The really great men must, I think, have great sadness on earth"
"Nothing in this world is harder than speaking the truth, nothing easier than flattery."
"Taking a new step, uttering a new word, is what people fear most."
"Much unhappiness has come to the world because of bewilderment and things left unsaid"
'Crime and Punishment' explores the elusive question of whether our choices have inherent substance or simply reflect cause and effect. It is a must.