Fiction - Molon Labe! by Boston T. Party
The only way I can describe this book is "Ayn Rand meets James Bond." It outlines a very plausible scenario in which libertarian activists, through technological savvy and strategic organizing, completely take over the state of Wyoming.
However, this isn't by any stretch a dry or staid polemic about liberty; it's action-packed and very exciting. To top it all off, Molon Labe! has inspired more than a few people to actually try and implement Boston T.'s plan.
I can't recommend this book enough, both for its merits as a "how-to guide" for libertarian activists, and for its sparkling originality as a political thriller.
--------------------------------------------------------
Non-Fiction - No Treason by Lysander Spooner
I'm not even going to try and explain this one, because there's no way I could do it justice. Suffice it to say that more than a hundred years after it was written, the ideas contained in this myth-shattering essay are just as shocking, challenging, and "dangerous" to the ruling elite now as they were upon the book's release.
No Treason can be read (or listened to) for free online, and really doesn't count as a *book* since it's not even 100 pages long. But I would be remiss if I didn't mention Spooner's magnum opus at every available opportunity.