intro
The internet has many sites for free books, often specialized. See:
Bookmarks / Research / Books & Journals online / Kindle
If one of these turns out to be helpful, I'll list specifics below.
http://www.booksshouldbefree.com
1/27/14 Found ebooks for The Last Days of Socrates (in separate parts)
Originals are from project gutenberg
Amazon has many free e-books for prime subscribers, but there does not seem to be a way to filter for free e-books. There are "helper" sites that seem to do so, though.
Most of this site at gizmo's freeware is devoted to Amazon sites (though additional links at the end)