Ludwig von Mises Institute
The home of Austrian Economics, the Institute’s online library has a huge collection of books on economics, politics, philosophy and law. Most of the material is in pdf format, rest in html. The books, papers and essays include those by authors such as-
Foundation for Economic Education
FEE’s Freedom Library has a few books on economics, politics and law, most notably, Henry Hazlitt’s book – “Economics in One Lesson”.
The Liberty Fund’s Online Library of Liberty has a substantial offering on subjects such as economics, political theory, philosophy, religion, law, literature. To browse its books by collections to which they belong, visit this page.
Internet Archive’s Text Archive has the biggest collection of online books (a million plus) of them all, and in multiple languages. The books are scanned copies of public domain books from various participating libraries. IA also hosts books from the Million Book Project.
Note on IA:
When you search for a book and click on a result, you are led to the book’s page – Theodor Gomperz’s Greek Thinkers (Volume 4), for example. To download the djvu version, follow the link that says “All Files: HTTP”, and you will be led to this page. From the various versions listed, select and download the djvu version.