My favorite authors

David Zindell:  Neverness, The Broken God, The Wild, War in Heaven
Zindell's books besides being excelent science fiction, are really philosophical works and almost exactly the philosophy I would write, so basically I can't recommend them highly enough.  If you want excellent thought provoking sci-fi or you want to know what I think about life the universe and everything then read this series.
There are two fan sites for Zindell which are linked to each other so you only need click on one, they are Beyond Nevernessand  Seekers of the Ineffable Flame .  Here are the qutotations that open each chapter for the four books.
 

Milan Kundera:   The Unbearable Lightness of Being, The Book of Laughter and Forgetting, Laughable Loves

Frecrich Nitzsche: Thus Spoke Zarathustra

Herman Hesse:
 Heese
Chogyam Trungpa:  Shambhala: The Sacred Path of  the Warrior
Shambhala     bio

Robert Heinlein: Stranger in a Strange Land
Heinlein is one of the foremost writers of science fiction, and while many of his books contain interesting philosophical ideas, many of them on human sexuality,  I find Stranger by far the most interesting and best written.  For review look  here or follow this link for more info on Heinlein.   Some quotes from the novel can be found here.
 

Robert Pirsig  Zen and the Art of Motorcycle Maintenance

Douglan Adams  Hitch Hiker's Guide to the Galaxy ,

Kurt Vonegutt:

Micheal Focoult: History of Sexulaity Vol 1-4

David Brin: Startide Rising, The Uplift War, Earth

Oscon Scott Card: Ender's Game
 offical website
Martin Buber:

Carlos Casteneda:

Dan Simmons: Hyperion, The Fall of Hyperion, Endymion, The Rise of Endymion