The Feynman Lectures on Physics,by Richard P. Feynman, Robert B. Leighton and Matthew Sands 

Essential Mathematica for Students of Science,Tutorial Approach to Mastery of Mathematica by James J. Kelly, Department of Physics, University of Maryland

The American Institute of Physics History of Physics List of Exhibits

Teaching Physics with the Physics Suite by Edward F. Redish

Physics Problem-Solving Strategies
Solving Problems in Physics by Dan Styer of the Oberlin College Physics Department
Teaching Introductory Physics Through Problem Solving by Ken Heller of the University of Minnisota School of Physics and Astronomy

Computer Algebra Programs
Maxima Freeware
Quickmath On-Line

Data Analysis and Uncertainty Calculations
The University of Toronto Chemistry Department has posted a well-written Stats Tutorial.

Textbook Revolution
A site started by Jason Turgeon with links to free on-line textbooks.

Energy: What it IS, What it is NOT, and How We Know
A web page with a bunch of Flash Movies by Walter Scheider

Physics Education Technology (PhET)
University of Colorado at Boulder physics simulation applets.

Interactive Experiments in Gravity
This site of John Walker, coauthor of AutoCad, shows how to construct a device for demonstrating the gravitational force of attraction between objects that you can hold in your hand and time-lapse videos of the apparatus in operation.  At the same site there is an applet that allows you to explore orbital motion.

Circuit Simulator
John Falstad has created a sophisticated circuit simulator java applet that allows you to build your own simulated circuits.  It depicts current as dots moving about the circuit in the direction of conventional current.  If you prefer current to be depicted as dots moving in the direction of electron flow, you'll probably want to use the Circuit Construction Kit at the University of Colorado Physics Education Technology (PhET) project web site.

The Intuitor Basic Physics Savvy Quiz
A conceptual physics quiz consisting of 40 true/false questions.  While you might think of a quiz as an evaluation tool, this one is an excellent learning tool because of the thoroughness of the feedback provided for each question (and because of the quality of the questions themselves).  The feedback becomes available after you submit your answers.

Geophysical Properties
g at Your Latitude and Longitude made available by the U.S. National Geodetic Survey is a calculator of the magnitude of the acceleration (relative to the surface of the earth) of an object in freefall (neglecting force of air) near the surface of the earth at a location having the coordinates you enter.  (Leave the elevation blank if you don't know it and the calculator will provide the elevation at the surface too.)  If you don't already have them, you can obtain the coordinates and elevation of the location of interest by means of the maps at http://www.topozone.com.  With the coordinates in hand, you can also get the properties of the earth's magnetic field at the same point on the earth by visiting the Compute Earth's Magnetic Field Values calculator made available by the United States National Geophysical Data Center.

NIST Reference on Constants, Units, and Uncertainty
Information on SI units and related topics from the United States National Institute of Standards and Technology.

Physics Documents by John S. Denker
A collection of explanations which in most cases were written as answers to questions posted on PHYS-L, a list serve for physics educators.

Donald Simanek's Physics Abused Web Page
A collection of documents written by Donald Simanek on physics misconceptions and incorrect explanations along with his own explanations and links to web sites with similar information.

University of Minnesota Physics Education Research and Development
Some of the best resources for learning and teaching physics can be found at the web sites of groups that do research into how people learn physics and research on successful methods of teaching physics. The University of Minnesota Physics Education Research and Development web site includes information on what works in physics education, useful resources for teaching your own course (e.g. the Context Rich Problems), and a comprehensive set of links to other physics education research web pages.

Physics Tutorials by James L. Hunt, Professor Emeritus,
University of Guelph, Guelph, Canada
Professor Hunt has created a of HTML-coded physics tutorials. The set, Physics Tutorials, is designed to enhance the user's introductory-physics-related mathematical skills as well as the user's understanding of some introductory physics concepts. 

Physics Books by Benjamin Crowell
Dr. Benjamin Crowell of Fullerton College has written three excellent introductory physics textbooks, all of which are available on-line in pdf (and other formats). He's also been a big promoter of free on-line books written by other people (check out his on-line book review site, The Assayer ). By means of his work, Dr. Crowell inspired me to write Calculus-Based Physics, and, through email communication, Dr. Crowell gave me the encouragement and information I needed to release it under a Creative Commons license.Here is a page with  links to the books he wrote:  Light and Matter

Peer Instruction Materials, Eric Mazur, Harvard University
I consider myself to be an extreme user of Eric Mazur's peer tutoring method. To me, the heart of the method is the execution of the reading assignment, by the students, prior to class. (In fact, I wrote my book in an attempt to maximize the reading of assigned textual material by my students. My thinking was, the shorter I could make a reading assignment, subject to the condition that it still contained the information I wanted the students to get out of it, the more likely the students would be to complete the reading assignment. I teach at a quality liberal arts college and the anecdotal evidence I have indicates that my students are getting more than 200 pages per week in reading assignments outside of physics.) Except for the occasional pop no-quiz, I start each class with a quiz. I aim for two questions that anybody who does a reasonably thorough job on the reading assignment will answer correctly, and one that requires application of the concepts covered by the reading assignment. After the quiz, I display a multiple choice question on a screen at the front of the room. The students respond, all at once, either by means of colored index cards, or, more recently, by means of the infrared transmitters of a classroom response system. What we do in class prior to the next question (discussion with peers, explanation of reasoning by a student, clarification of the concepts by me, a second opportunity for students to answer the same question, or nothing) depends on the responses. We deal with such multiple choice questions, one after another, until we run out of time. I make up some of the questions and the others are concept tests that come with Peer Instruction: A User's Manual, by Eric Mazur. 

Other Free Textbooks
Go to Tech books for free and click on the Science tab to see a strong list of free science and engineering books. James Nearing's Mathematical Tools for Physics looks particularly useful to me.

Sonoma State University Department of Physics and Astronomy
Dr. Joseph Tenn of the Sonoma State University Department of Phyiscs and Astronomy hosts a series of invited talks at Sonoma State and is now making them available in streaming video at What Physicists Do .  At that site, the talks can be viewed live at 4 pm (Pacific Time) on Mondays during the academic year, or after the presentation.  I recommend the Feb. 06, 2006 talk SEEING THE INVISIBLES: THE CHALLENGE TO PARTICLE PHYSICS IN THE NEW MILLENNIUM  by Prof. Hitoshi Murayama. 

SciLab
The computer program SciLab provides an interpreted programming environment similar to MatLab, but SciLab is free.  It is useful for solving introductory physics problems for which either the analytic solution is beyond the scope of the course, or, there is no analytic solution.  (Finding the trajectory of an object for which air resistance is not negligible would fall into this category.)  The quick and easy generation of graphs in SciLab is particularly valuable.

The Andes Physics Tutor
The Andes Physics Tutor is a free on-line homework system in which students construct diagrams, select the applicable concept and otherwise work out the solutions to physics problems with feedback at every step.