Free physics books are found on the web as frequently as birds are found in aquaria. Here are the best ones.
For learning physics for examinations, an excellent site is Hyperphysics at hyperphysics.phy-astr.gsu.edu/hbase/hframe.html.
The high-quality electrodynamics text by Bo Thidé, Electromagnetic Field Theory, can be found at www.plasma.uu.se/CED/Book.
Two excellent introductory physics texts by Benjamin Crowell, Simple Nature and Light and Matter, as well as a textbook on calculus and a textbook on general relativity can be downloaded at www.lightandmatter.com.
The extensive Encyclopedia of Earth, covering geology, geography, ecology, biology, paleontology and much more, written by many professional authors, is available at www.eoearth.org.
A list of internet links to physics lecture notes and to a large spectrum of physics information can be found in Volume I of the Motion Mountain Physics Text, in Appendix C: Sources of information on motion. Additional specialized websites are given throughout the text. They are all clickable in the pdf version of the text.