Ayn Rand of course! Both her fiction (Fountainhead, Atlas Shrugged, We The Living, Anthem, etc.) and non-fiction (Virtue of Selfishness, Capitalism: The Unknown Ideal, Philosophy: Who Needs It?, etc.).

"The Grapes of Wrath" ...It is as important to understand the human impact of the Great Depression as it is to learn about the interventionist economics that caused it.

The Bible - NIV application bible is my fav

National Suicide - Martin Gross

What Americans Really Want...Really - DR Frank Lutz

I think An Enemy of the State: The Life of Murray N. Rothbard by Justin Raimondo is a great look into the history of libertarianism in the 20th century, not to mention the life of one of the greatest thinkers of our time.

Hidden Order - David Friedman

The above suggestions are great reads. Here are a few more:

We  -Zamyatin (Fiction)

They thought they were free -Mayer

No Treason -Lysander Spooner

I Must Speak Out: The Best of The Voluntaryist -Watner

What has Government done to our money? -Rothbard

Machinery of Freedom- Friedman

For a New Liberty: The Libertarian Manifesto by Murray N. Rothbard

Tom Baugh's book Starving The Monkeys is a must-read, must-share

.

Add The Market for Liberty by Linda & Morris Tannehill to the list. Explains in great detail how a stateless society could & would function, but easy to read & follow. 2nd on my list. For a New Liberty by Rothbard being #1

Walter Block - Defending the Undefendable

Thomas DiLorenzo - Lincoln Unmasked 

Andrew Napolitano - Lies the Government Told You

My personal top 3 would be:

Ron Paul- "The Revolution: A Manifesto"

Harry Browne- "The Great Libertarian Offer"

Murray Rothbard- "For a New Liberty"

Those books all changed my life in significant ways, and I recommend them highly to anyone interested in libertarianism.

I highly recommend the new book 'Libertarianism Today' by Jacob Huebert

Here is a presentation that helps to explain the current fiscal situation, I think this presentation helps to draw in many people in the scientific fields. The presenter claims to be an Austrian, with limitations - and uses a lot of data by applying it through applied science, a combination of physics and economics! Not sure if the video applies to this post but it's worth the watch for everyone.

http://outerdnn.outer.jhuapl.edu/rethinking/VideoArchives/MrJamesGRickardsPresentationVideo.aspx

Human Action: A treatise on economics  Ludwig Von Mises

Three Cups of Tea by Greg Moretnson, why you might ask? Very simple...private peace efforts go a long way to combat terrorism, and many have said that Mr, Moretenson by going over to Pakistan and Afghanistan and building schools for children there has done more to combat terrorism than American military operations. This book is a real world story on, as Tony Stark in Iron Man 2 put it "privitizing peace"

Also, the essay "Persuasion vs. Force" by Mark Skousen is excellent!

Naomi Klien - "The Shock Doctrine" I know, she is a lefty, but this book will show you how horrible Friedman's Chicago School actually is.

John Perkins- "Confessions a an Economic Hitman"

Suzanne Collins - "The Hunger Games Trilogy" Just finished this for some good light fiction reading. Lots of liberty oriented ideas, and the coniving ways that politicians exploit others. I was able to read the whole trilogy in like 2 weeks, its a quick one.

To add just another post to back it up - Murray Rothbards "For a New Liberty: A Libertarian Manifesto" For all you minarcists this is or perhaps Mary Ruwarts "Healing our World" will answer many questions you might have of your anarchist brothern

Agree with Healing our World.

Civil Disobedience by Henry David Thoreau

I think it would be helpful to split this up by subject matter and difficulty, as Bonnie suggested.

Economics:

• Beginner--Economics in One Lesson
• Intermediate--An Introduction to Austrian Economics, Thomas C. Taylor
• Advanced--Man, Economy, and State (this is a better book to learn economics from than Human Action...Rothbard originally intended it as something like a textbook, although it grew beyond that)
• Extra Credit--Human Action by Mises, America's Great Depression by Rothbard

Anarcho-capitalism:

• Beginner--Chaos Theory (Robert Murphy)
• Intermediate--I've got nothing.
• Advanced--The Market for Liberty
• Advanced--For a New Liberty (Rothbard)
• Extra credit--Lysander Spooner, Albert Jay Nock

Classical Liberalism/Paleoconservativism/etc

• Beginner--I'm drawing a blank...maybe one of the Politically Incorrect guide series? Maybe you just need to jump in and read the Enlightenment-era texts?  Heck, maybe just read the Declaration of Independence and the Bill of Rights?
• Intermediate--Bastiat, The Law
• Advanced--Locke, Two Treatises on Government (mostly the second)
• Advanced--Burke, Reflections on the Revolution in France (the first half)

Central Planning:

• Beginner--I, Pencil by Leonard Read
• Intermediate--The Use of Knowledge in Society by Hayek
• Advanced--Economic Calculation in the Socialist Commonwealth by Mises

"Modern" Philosophy:

• Intermediate--a few chapters from The Virtue of Selfishness by Rand (probably skip the stuff by Nethaniel Branden [spelling?])
• Advanced--Anarchy, State, and Utopia

Fiction:

• No real "levels" here...
• 1984
• Brave New World
• We
• The Moon is a Harsh Mistress (Heinlein)
• Atlas Shrugged
• I might add that the anime Tengen Toppa Gurren Lagann is insanely libertarian, although anime's a bit niche for some people.  Know your audience.  Deals with the contrast between heirarchical/coercive and individualist/voluntary responses to crises.

Nonviolence and political change:

• Intermediate: From Dictatorship to Democracy by Gene Sharp (http://www.aeinstein.org/organizations98ce.html) and the history/introduction to the same (http://www.aeinstein.org/organizations/org/FDTD_history.pdf)
• Intermediate: Discourse on Voluntary Servitude by Boetie

Miscellaneous:

• The Road to Serfdom, Hayek
• mises.org's extensive free economics literature
• reason.org and Reason magazine.

"The Constitution of Liberty" by Hayek is stellar.

The Giver and Gathering Blue by Lois Lowry are both excellent on collectivism and property rights, respectively...

I'd suggest The Alaskan Bootlegger's Bible for when you're not busy reading. Gotta have a hobby.