I maintain a large online library of documents of interest to pilots, from students to experienced aviators and instructors.
You may also want to visit my blog, where I post articles for pilots on a variety of topics, such as tips on using advanced avionics, changes in regulations and policy, and answers to questions that I see on aviation forums.
The online library includes PDFs of FAA training handbooks, advisory circulars, pilot guides for popular avionics, and many other resources.