I'm not really picky when it comes to learning something. Some of my favorite books are:
What if? 2
There's a book series written by Randal Munroe called "What If? that I absolutely love.
In one of the chapters there's a question posed about how many caleries a T-Rex needs to survive.
Apparently about 80 burgers or so.
The Mad Man's Library
Another book I enjoy is called The Mad Man's Library. There are so many cool and fascinating things in the book.
However, it may not be for everyone. What I enjoy most of all is the historical context from the book.
An Underground Education
This book covers interesting facts ranging from medicine, science, history, and crime.