Hmm, that is a tough one. I've read a lot of good books, but not too often have I gone back and reread many of them. Mainly it's due to the time needed. If I had to pick some books that I would strongly recommend, I would go with:
The Chrysalids by John Wyndham - it's a fairly short sci-fi story. It's about world after some kind of disaster (you can figure out what it was if you read the book) and how society has regressed. A lot of it centres around conflict from society vs deviants/mutants.
The Amazing Adventures of Kavalier and Clay by Michael Chabon - this is a fantastic book. It's based on two characters starting up a comic book during the Golden Age of comics. If you haven't read it, you definitely should check it out.
The Once and Future King by T H White - this not the most true to myth version of King Arthur, but it's the best. It does a great job at giving a sense of wonder and magic in the earlier parts, before things progress to their inevitable end.
Jonathan Strange and Mr. Norrell by Susanna Clarke - it's set in the Napoleonic wars, in a world where magic is real, but faded. It does one of the best jobs at world building that I've ever seen. The book is filled with footnotes that have random tidbits and give a lot of depth to its lore.
