If you’re interested in Free Libre Open Source Software and would like some valuable reading material to become an expert, FLOSS Manuals is a great site.
You can find books about Blender, Inkscape, Firefox, OpenOffice, Audacity, WordPress, Linux Command Line, to name a few. Find the manual you want, read it on their site, download, or order a printed copy. Only the printed copy is not free.
Also cool is the ability to remix your book to get only certain chapters that you find interesting.
Go there, get some nice reading material and even help out by being a writer or a proofreader.