Anarcho-capitalism is a funny, kooky li'l ting. Folks have been nifty enough to create wiki articles not only for anarcho capitalism overall but for each of its core concepts as well. One also gets an excellent all-round summary from Bryan Caplan's FAQ.
From that FAQ's list of anarchist texts I have identified those which you must read to understand anarcho-capitalism, autarchism, voluntaryism, or whatever we're supposed to call it. They are presented in order of publication below. The last of the six on this list is not free.
The Production of Security by Gustave Molinari
The State by Franz Oppenheimer
The Market for Liberty by Morris & Linda Tannehill
For a New Liberty by Murray Rothbard
The Machinery of Freedom by David Friedman
The Problem of Political Authority: An Examination of the Right to Coerce and the Duty to Obey by Michael Huemer
Below are two empirical works that offer real examples, in detail, of stateless law / private law / polycentric law. Neither of these are available for free.
The Enterprise of Law: Justice Without the State by Bruce L. Benson
The Law of the Somalis by Michael van Notten
And there's a general reference point for finding ancap anything now!