the meditations of marcus aurelius - for the what is a good person, he really hits the nail on the head, waste no more time debating about what a good man should be, be one(or something along those lines, its been a while) platos republic - mainly for the cave beyond good and evil friedrich nietzsche - for the moral relativism rhetoric by aristotle (i read a book a long time ago on dishonest rhetoric but i cant remember the name, that book was fantastic if you can find it) while there is no books about diogenes he is one of my favourites and its worth looking up the stories about him for some funny bits of history same for Alcibiades although if you are using these for home schooling you may want to leave out his early life as Socrates bum boy and im not even joking that is a thing it would be a real same to limit your self to western philosophy some of the greats come from the far east, lao tzu(book of the dao) and sun tzu(Art of war) are certainly some of the great philosophers and personally im a big fan of the Daoist, lao tzu is one of the smartest people to have ever lived, i cant really put in to words as to why but you may see what i mean if you give the book of the dao a read, really that mother fucker got the creation of the universe right 4000 years ago(at least) if you want more modern stuff kierkegaard did had some interesting ideas and while i have not personally got around to him yet i have heard good things about Ludwig Wittgenstein edit; oh and the prince by Machiavelli, the dude gets a bad reputation but its pretty undeserved edit; for fiction or maybe allegories would be the best word, terry Pratchett, the dude was extremely smart and contributed more to science and philosophy than many scientists and philosophers, i will not bother naming a book because all of them are good, the same thing for douglas adams a lot of the old scifi is also worth a read, Asimov, arthur c clark, jules verne, orson scot wild, larry niven, robert a heinlein are all good