Ludwig von Mises Institute
This is a great source for books about Austrian economics, and liberty in general. Click on the "Store" section on the website.
The Cato Institute
This is the website for the publications from the most famous libertarian think tank. Cato does excellent work on liberty issues, and you will often find their people quoted by the press. Check here for scholarly articles on current issues touching on liberty.
Amazon.com
This is the premiere online bookstore in the universe. If a book is still in print, they likely have it. They probably also have a review or two. If you haven't tried them, you are missing a treat.
mail comments to burger@burger.com