http://en.wikipedia.org/wiki/Project_Gutenberg It is, simply, a huge listing of public domain ebooks.
In the spirit of IslanderNL's Nov 17 posting about the Loomis PDFs (really, thanks
Speed, Harold - The Practice and Science of Drawing http://www.gutenberg.org/etext/14264
Maginnis, Charles, 1867-1955 - Pen Drawing An Illustrated Treatise http://www.gutenberg.org/etext/17502
Gutenberg http://www.gutenberg.org/wiki/Main_Page is an American (US) site, so the copy right laws would change accordingly. Just make sure you check out the local laws... or find someone that can translate them.
http://pge.rastko.net/ http://www.lonnrot.net/ http://gutenberg.net.au/ http://www.gutenberg.nl/
http://www.gutenberg.ph/
If you find a book that you think might interest others... post about it.