Miguel De Cervantes 'Don Quixote'
Cervantes believed that a good novel should have a touch, a dusting, of everything. It should combine elegantly all the possible types of story. Dostoyevsky called it "the ultimate and most sublime work of human thinking" and so I guess, the proof is in the pudding.*
*one of many popular modern phrases coined by Cervantes' famous Knight.
Dialogues of Plato.
Although often difficult to dictate who's voice leans closest to the surface, Socrates or Plato, the dialogues encompass the true foundation of greek thought. With apologies, pun intended, to Aristotle's more influential 'Nicomachean Ethics' this is the essential first reading. Of course you will find many versions of the Dialogues, as they encompass all platonic writings, from Apology through to Republic, Symposium and later works. Focus early on the more Socratic thinking, Meno and Phaedo are my personal favourites.
** you will always find the Dialogues as selected works, for something more fundementally Plutonic read 'Republic'.
John Steinbeck 'East of Eden'
Steinbeck's finest work, at least in my opinion. A true American writer in the mould of other favourites Twain and Kerouac, 'East of Eden' is the novel Steinbeck is most proud of, seeping in allusion, philosophical sentiment and the dynamic of good and evil. Although fantastic, it can seem out of touch with reality in his effort to make the deeper meaning stand out, because of that it loses the cultural relevance of earlier works 'The Grapes of Wrath' and 'Of Mice and Men'.