General Physics Sites

The Exploratorium
Physics 4 Kids
Phet - Free Online Interactive Simulations from the University of Colorado at Boulder.

Forces

Engineering Interact Animation that shows gravity, friction, compression, stretching and magnetic forces in a fun way, at 'Parkworld', an amusement park.
Fossweb - Force and Motion from the Full Option Science System

Simple machines

Inventors Toolbox - The elements of machines (phots and descriptions) including sketches from Leonardo Da Vinci.
Gadget Anatomy - a short quiz about the simple machines that make up more complex machines.
"If Simple machines were not around...?" - a worksheet for students
Simple Machines game from the Museum of Science and Industry

Energy

Energy Quest - Science projects about energy.

Electrical Circuits

Flash animation to create circuits

Light

Optical Illusions
Change Blindness - an optical phenomena that causes the observer to miss changes in two images when flashed on a screen.

Sound