All works with a download button can be downloaded directly and free of charge as PDF from hoppeunplugged.com.
This major work by Ayn Rand (1905-1982) has probably won more Americans to the libertarian cause than any other publication. In 2009, for example, half a million copies sold, and even Obama had a "Rand period" in his youth - though unfortunately without a lasting impact.
the ethics of liberty
"The Ethics of Liberty" also argues for a stateless society but from the perspective of a natural righs philosopher. Murray N. Rothbard (1926-1995). was Hoppe's friend and mentor. The book is clear, concise and easily understandable if you stay focused. The book has an excellent English audio version.
the problem of political authority
"The Problem of Political Authority, An Examination of the Right to Coerce and the Duty to Obey". Michael Huemer (1969) is a professor of philosophy and "starts from moral premises that most non-libertarians already accept" (Bryan Caplan). The book, thus, offers a "conventional" path into the libertarian world. The author's youtube reviews provide good overviews.