Essentials of Economics - a brief survey of principles and policies
by Faustino Ballvé

Free PDF! http://mises.org/books/ballve.pdf

and of course
The Road to Serfdom
by Friedrich A. Hayek

Also Free PDF! http://mises.org/document/2402/The-Road-to-Serfdom

Disclaimer: there's no such thing as a free book!