Two books top my favorite of all time from my collection of non-fictions. Each one is a great read that is worthy of anyone's collection: The Selfish Gene by Richard Dawkins and Guns, Germs and Steel by Jared Diamond. I learned a great deal from these books.

Two of the best Computer Books I ever read are,
The Design of the Unix Operating System by Maurice J. Bach (timeless classic)
C++ for Real Programmers by Jeff Alger (this is NOT your average language book)
Even if you don't need to learn Unix or C++, you can read these books for the sheer intellectual challenge and satisfaction. I got hold of the copy of the Unix book right out of college in 1991, I still treasure it. The C++ book, I incidentally got it from the UNC library for course work, I loved it so much, I bought a copy.

Other books I like from my collection:
The Code Book by Simon Singh
The Origins of Life by John Maynard Smith
Newton's Gift by David Berlinsky
To Infinity and Beyond by Eli Manor
The Story of √-1 by Paul J. Nahin
Zero by Paul Seif
First They Killed My Father by Loung Ung

I have this habit of voluntarily lending the books I like to our friends. Luckily most of them return it, even when I loose track. Nowadays, I keep a log :-)