Sci-Fi & Fantasy (by authors):
(Epic)
J.R.R. Tolkien
Robert Jordan
Steven Erikson
(Series)
C.J. Cherryh
L.E. Modesitt
Kate Elliot
Katherine Kerr
J.V. Jones
Tad Williams
Raymond Feist
Janny Wurts
Mercedes Lackey
(gets a little formulaic after a few trilogies, but still enjoyable)
(Comedy)
Terry Pratchett
Douglas Adams
Spider Robertson
(Other)
Iain M. Banks
Robert A. Heinlein
Non-Fiction:
(Reference)
"Ideas" by Peter Watson
"A World of Ideas" by Chris Rohmann
(On Civilization)
"Guns, Germs, & Steel" & "Collapse" by Jared Diamond
"The Limits to Growth" by Meadows, et al
"The Collapse of Complex Societies" by Joseph Tainter
"The Upside of Down" by Thomas Homer-Dixon
"The Geography of Nowhere" by James Howard Kunstler
"A Short History of Progress" by Ronald Wright
(Also see others in the CBC Massey Lecture Series; most are very good & not all fall under this categorization.)
(Economics & Game Theory)
"Happiness" by Richard Layard
"The Origin of Financial Crises" by George Cooper
"The Origin of Capitalism" by Ellen Meiksins Wood
"Confessions of an Economic Hit Man" by John Perkins
"Small is Beautiful" by E. F. Schumacher
"The Complexity of Cooperation" by Robert Axelrod
"The Misbehavior of Markets" by Benoit Mandelbrot & Richard L. Hudson
"The Winner Take All Society" by Robert H. Frank & Philip J. Cook
"Shop Class as Soul Craft" by Matthew B. Crawford
(More of an extended essay on the nature of work in modern society, but without question an excellent read.)
(Elinor Ostrom also belongs on this list, although so far I've only read summaries of her work. She recently won the Nobel Prize in Economics for research on informal, cooperation-based solutions to the problem of the tragedy of the commons that don't rely on either privatization of property or management by governments.)
(Biology, Ecology, & Evolution)
"The Making of the Fittest" & "Endless Forms Most Beautiful" by Sean B. Carroll
"The Web of Life" by Fritjof Capra
(Nonlinear Dynamics for Dummies)
"Chaos" by James Gleick
"Complexity" by M. Mitchell Waldrop
"Emergence" by Steven Johnson
(Cognition)
"Language In Action" by William Turnbull
"Philosophical Investigations" by Ludwig Wittgenstein
(Well, since it's virtually incomprehensible, mostly just read the SparkNotes.)
"Intelligence With Representation" by Luc Steels
(This is actually a paper, not a book, but definitely worth reading since he solves the grounding problem of symbol systems. There are a few caveats, but I will only go into those if someone asks for them; this post is too long already.)
"The Quantum Brain" by Jeffrey Satinover
"Predictably Irrational" by Dan Ariely
"Kluge" by Gary Marcus
"The Brain That Changes Itself" by Norman Doidge
"Descartes' Error" by Antonio Damasio
"The Social Atom" by Mark Buchanan
(Religion)
"The Lost Gospel of Judas Iscariot" by Bart D. Ehrman
Okay, I think I'll stop there, since that should keep most people going for a few years!
(There are others that I'm tempted to recommend because they look like they'll be really good, but I have restricted myself only to books/authors I've actually read, with just that one exception.)