I picked up mathematics, physics and philosophy. I would recommend these to anyone who doesn't have a list of principles, theories, and laws on hand.
I am reading the physics one now. There is everything from Mach's principle to Absolute Zero- Newton's theory of color to General relativity- String theory to cosmic inflation. So far it has been a good read- short, direct and to the point.
I found these at Walden books for about 5 USD a peice. I also found Essential Einstein, Universe, A Brief History of Time, Universe in a Nutshell, Stem Cell Now, and The Scientists. I only paid 60USD for all of them!