I like many of Marion Zimmer Bradley's works. They're VERY long, but the following are worth getting through:
I recently bought THE FIREBRAND (reading it now) and THE MISTS OF AVALON from Amazon.com--I'd read them both years earlier (library copies). The first is a retelling of the Trojan War from the perspective of the princess/prophetess Cassandra (spelled Kassandra in the book). The second is a retelling of the Arthurian legend from Morgan le Fay's perspective.
I also read THE FOREST HOUSE (Roman invasion of the British Isles) and THE FALL OF ATLANTIS.
Other authors: Jim Butcher's DRESDEN FILES series, Neil Gaiman/Terry Pratchett's GOOD OMENS, Douglas Adams' HITCHHIKER'S GUIDE series.
I read SINGULARITY by William Sleator in middle school. Definitely a YA book, but still very good.
I also liked STRANGER IN A STRANGE LAND, DUNE, 1984, BRAVE NEW WORLD, FAHRENHEIT 451, SLAUGHTERHOUSE-FIVE...what else...I read PODKAYNE OF MARS (I think that's by Heinlein) once, but don't remember it very well.
Oh, and finally (though this is technically horror), anything by H.P. Lovecraft.
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The existence of the leader who is wise
is barely known to those he leads.
He acts without unnecessary speech,
so that the people say,
'It happened of its own accord.' -Tao Te Ching, Verse 17