If available, the names of the books are linked to Amazon.com. If not, they are linked to another bookstore.

Existential Theory

Psychoanalysis and Daseinsanalysis, by Medard Boss   
Existential Foundations of Medicine and Psychology, by Medard Boss
Man’s Search for Meaning, by Viktor E. Frankl
Being and Time, by Martin Heidegger
Existence, edited by Rollo May, Ernest Angel, Henri Ellenberger
The Meaning of Anxiety, by Rollo May
An Introduction to Husserl’s Phenomenology, by Jan Patocka
The Courage To Be, by Paul Tillich
Existential Psychotherapy, by Irvin D. Yalom
Theory and Practice of Group Psychotherapy, by Irvin D. Yalom

Miscellaneous

A General Theory of Love, by Thomas Lewis, Fari Amini, & Richard Lannon
Men Are From Mars, Women Are From Venus, by John Gray

String Theory

The Elegant Universe, by Brian Greene
Parallel Worlds, by Michio Kaku

Neurology: Brain Studies

Welcome to Your Brain: Why You Lose Your Car Keys but Never Forget How to Drive, by Sandra Aamodt and Sam Wang
Mind Wide Open: Your Brain and the Neuroscience of Everyday Life, by Steven Johnson
The Creating Brain, by Nancy C. Andreasen
Inside the Brain, by Ronald Kotulak
The Brain, by Richard M. Restak
The Brain has a Mind of its Own, by Richard Restak