how to be happy: The How of Happiness by Sonja Lyubomirsky, Stumbling on Happiness by Dan Gilbert
behavioral economics: Predictably Irrational, by Dan Ariely
emotions: Emotions Revealed, by Paul Ekman
depression: The Mindful Way Through Depression, by Jon Kabat-Zinn et al
mindfulness/living in the moment: Wherever You Go, There You Are, by Jon Kabat-Zinn (see also my article on the topic)
evolutionary psychology: The Moral Animal, by Robert Wright
health: Anticancer, by David Servan-Schreiber
getting along in relationships: How to Avoid Marrying a Jerk, my article on the topic
learning/mastery: The Art of Learning, by Josh Waitzkin