http://www.booksshouldbefree.com/book/on-the-duty-of-civil-disobedience-by-henry-david-thoreau
Lots of free audio books including Thoreau.... :)
and architecture....
http://www.booksshouldbefree.com/book/on-architecture-by-vitruvius
Above downloadable including pix
http://books.google.com/books?id=QEotAAAAIAAJ&dq=By%3A%20Marcus%20Vitruvius%20Pollio%20(Vitruvius)&pg=PA28-IA2#v=onepage&q&f=false