http://www.nist.gov/index.html National Institute of Standards and Technology. You name it - health, materials, energy, nanotechnology, chemistry, physics, math etc. information.
http://www.physicsclassroom.com/index.cfm Classrom tutorials, multimedia, shockwave, practice reviews and more
http://www.physics.nist.gov/cuu/Constants/index.html NIST Fundamental Physical Constants
http://hyperphysics.phy-astr.gsu.edu/hbase/hframe.html An understandable HyperPhysics index
http://dir.yahoo.com/Science/Physics/ Extensive links for all things related to physics - relativity, quantum, theoretical and amusement park ride physics