I also would recommend a sci-fi triolgy by C.S. Lewis, the names of which are "Out of the Silent Planet, Perelandra, and That Hideous Strength ". I really enjoyed those books.
Yes, these are great too.
I forgot to mention too the Asimov books that are 'sort of' in the Foundation universe like End of Eternity - that is a great read. All the robotic short stories (like the one I Robot stole from) are good too.