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, can be downloaded at www.lightandmatter.com.
The interesting Biophysics Educational Resources, edited by Victor Bloomfield, can be found at www.biophysics.org/education/resources.htm.
The text Classical and Quantum Chaos, by Predrag Cvitanovic, Roberto Artuso, Per Dahlqvist, Ronnie Mainieri, Gregor Tanner, Gábor Vattay, Niall Whelan and Andreas Wirzba is available at chaosbook.org.
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 Excursion C of the Motion Mountain physics text.