I came across this site, Textbook Revolution whilst browsing for freebies. Tom Kyte wrote about free stuff that he uses and I went and browse through my own free stuff.
Anyhow, I have not yet browse thoroughly through Textbook Revolution yet but some stuff already look promising. For example, the following free online course on Enterprise Security is something that I'm interested in and over the next few weeks will try out the course.
Granted that not all the free books are totally currently but I would say a good portion seems to be at least a couple of years (2003) and should still be valid for basic concepts and minor updates to syntax and language.
Obviously if you find any links to copyrighted materials, please feel free to contact the webmaster of Textbook Revolution so that they can be removed. It would be a shame to see this wonderful resource shut down because of one bad link.