Physics Database (http://physicsdatabase.com) is making available hundreds of science books for free download. As would be expected, most are highly technical physics and math textbooks. They may be in PDF or HTML format.
Here is the list.
I'll be back after the holidays. In case you missed them, check out some of my earlier posts.
Does Ridiculing Climate Deniers Work?
How to Talk to the Public About Science - Lessons from Neil deGrasse Tyson
How the Media are Used to Intentionally Mislead the Public About Global Warming