Like Gizmos only with instructions for teachers as to how to use them in the classroom.
University of California College Prep Open Access. A good list of science courses. Online lab simulators are great fun to play with!
Math explanations plus classic games (Connect 4, chess, checkers, mah jong, etc.)
Fill in the blank to make addition equations to 5, 10, or 100. Lots of other games at this site.