You can download a number of chess books in pdf format from the following site: pdf-freedownload
Actually, this site is a bunch of links that direct you to other sites where you can view or download the books. In some cases they are old books nobody is likely going to want and in other cases they are “sample” downloads where you get 20 or 30 pages of a book from the publisher as an inducement to buy it. Many of the samples seem to be Eric Shiller books from Cardoza Publishing. From what I’ve read, most anything written by Schiller is not worth the price even if it’s free. Be that as it may, for example his book Development of a Chess Master contains 37 pages with some lessons in basic tactics…the book looks to me to be along the line of all those -------- For Dummies books. Also, some of the downloads are just catalogs.
There’s always a question about free downloads of chess books as to whether they are legal and violate copyright laws. Most sites won’t carry them if they are illegal, but some do. Bookyards is a Canadian website that follows Canadian copyright rules (far more lenient than US laws) but they still try to follow U.S. rules. Many sites don't adhere to Bookyard's standards.
Anyway, I give the link to this site in case anybody wants to poke around and maybe find something interesting.
EDIT 3-29-16...the link is now broken