Wolfram Science World: Encyclopedias of math, physics, astronomy and other sciences
Videos on challenging physics concepts supplied though NASA
This site contains interactive plasma physics topics, ranging from electricity, magnetism, energy, and fusion.
Articles and interactive activities provided by NSF
Physics Site Guide with resources and activities for educators, though useful to all undergraduate students as extra practice in physics coursesThe Physics Classroom: Interactive web pages and animations on a broad range of physics topics