The excellent new site Libertarianism.org  has put together this discussion with David D. Friedman on his book The Machinery of Freedom. It's a fascinating discussion of a topic many refuse to consider — whether the institutions virtually everyone, including libertarians, consider the preserve of the state, could instead be carried out by private organizations as well or better than the state. Friedman discusses private courts and police, as well as, for me, the toughest question of national defence. Has private supply of these goods ever worked well in history, or are these what we need a state to provide?
Some find this kind of discussion esoteric or utopian. Indeed, the sort of anarcho-capitalist who insists that it is wrong for a state to exist because it necessitates some violence can be frustrating. But conflating arguments made by the likes of Friedman with this kind of puritanism is silly. It's quite reasonable to ask whether the things that make markets superior to the state in some areas, like organizing people's economic activity, might also make markets better than the state in other areas, like providing law. And it's intellectually valuable: just as an understanding of how a free market would work is a useful starting point in real-world economic analysis, an understanding of how a stateless society might work can help us understand the state-heavy world we live in.
Incidentally, a roughly-typeset (but still very readable) version of Friedman's book is available online . He's hoping to do a third edition  of the book, if the peculiarities of copyright law don't stop him from doing so.