Kurzweil, Ray. The Age of Spiritual Machines: When Computers Exceed Human Intelligence. New York: Viking, 1999. A fascinating, optimistic look at thinking machines and uploaded minds; see also my dialog with computer scientist A. K. Dewdney about this book at www.sfwriter.com/brkurz.htm.

LeDoux, Joseph. Synoptic Self: How Our Brains Become Who We Are. New York: Viking, 2002. A good look at the neuronal nature of human minds.

Moravec, Hans. Mind Children: The Future of Robot and Human Intelligence. Cambridge, Massachusetts: Harvard University Press, 1988. A classic about artificial intelligence.

Ornstein, Robert. The Evolution of Consciousness: The Origins of the Way We Think. New York: Touchstone (Simon Schuster), 1991. Makes clear that Darwin has a lot more to teach us about consciousness than Freud.

Penrose, Roger. The Emperor's New Mind: Concerning Computers, Minds, and the Laws of Physics. Oxford: Oxford University Press, 1989. A classic proposing that human consciousness is quantum mechanical in nature.

Penrose, Roger. Shadows of the Mind: A Search for the Missing Science of Consciousness. Oxford: Oxford University Press, 1994. Among many other fascinating things, explores the possible relationship between microtubules and human consciousness.

Pinker, Steven. How the Mind Works. New York: Norton, 1997. A fine overview of modern cognitive science, mostly from an evolutionary-psychology perspective.

Richards, Jay W., ed. Are We Spiritual Machines?: Ray Kurzweil vs. the Critics of Strong A.I. Seattle, Washington: Discovery Institute Press, 2002. Precisely what the title says.

Searle, John R. The Mystery of Consciousness. New York: New York Review of Books, 1997. The originator of the "Chinese Room" problem cited in this novel spells out his beliefs about the ineffable nature of human consciousness.