Hewlett Packard: Hp's own experiment site has many good physics  experiments as well as some chemistry experiments.

Mad Scientist Library:  A great general science site with many experiments and information in all areas of science.

Amusement Park Physics: Learn about forces and motion while taking a ride in a virtual amusement park. Great fun

Back of an envelope: Learn about powers, scale and more. You don't need fancy equipment to teach physics.

Hands On Physics: An extensive unit on heat and temperature. Could be adapted for any grade level.

The Physics Classroom: Lessons on the major topics of physics such as force  and motion, movement, work etc. Good diagrams and an easy-to-follow format for each lesson.

Webster's World: An online tutorial created by highschool students for use by students.

Physlink: An online physics reference guide that is very well done.

A Century of Physics: A timeline for the last century of physics.

Physics Problems: Need to challenge your students? You should be able to with questions from this site.