Here's my 3:
How the Mind Works by Steven pinker
If you have ever wanted to know how you and other human beings function and get a look at your own hard-wiring, this is for you. I learned more in this book that from any other book I have ever read.
Life and How to Survive It by John Cleese and Robin Skynner
This book is written as a conversation between Monty Python's John Cleese and his psychiatrist. It is the first book I found that explains human psychology in terms of what is healthy behaviour (as against what's unhealthy or just plain wacko behaviour, leaving you to wonder what, then would be healthy). Very witty.
Everything I needed to Know I learned in Kindergarten by Robert Fulghum
Light and profound at the same time. Love Fulghum's books.
Any one of these books would make a great stocking filler if you're still looking for Christmas presents or want to suggest one you'd like to receive

PS: Here's a little stocking filler from me to you, a free e-book by Seth Godin:
http://sethgodin.typepad.com/files/what ... -now-1.pdf