Physics Central is a great resource for physics teachers and students from the American Physical Society. There are lesson plans, free resources, physics in action, profiles of people using physics, and much more. It is definitely one of the first places a teacher should go looking for physics resources.
The Physics Classroom - this is a great site for students. The site was actually created by students and is still maintained. The site has topics in lesson format, with descriptions, examples, demos, animations, videos, links, example problems, and practice problems, with solutions. I use it with my students as a study resource for them. There are also teacher lesson planning resources available.
PhysicsMedic - this is my web site (I teach physics and I am a paramedic). I have a lot of resources and links for my physics students on the site, including study guides, help guides, and physics and math help web sites.
Some other physics resources: