Doubtless there'll be lots of strong opinions, and (hopefully, usefully) lots of duplicates that you can then tote up to get a bit of a consensus. Iain M. Banks - all his Culture books are fantastic, but I'll single out 'Excession' since you seek titles. Neal Stephenson's 'Anathem' Stephen Donaldson (most famous for the Thomas Covenant tri-trilogy) wrote a 5-book 'Gap Series'. I have very fond memories of it, though it's been two decades since I read it. Philip K. Dick wrote a tonne of good stuff (and a bit of meh) but my two favourite are Clans of the Alphane Moon (the first Dick I read), and Valis (a bit more conventional to have on the favourite list) Ursula Le Guin also has a huge body of excellent work - Left Hand of Darkness, and The Dispossessed are my favourites. I really loved Roger Zelazny's Lord Of Light, though I understand it's not conventionally considered his best work.
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