There are a large number of teaching aids on the web. In fact, there are too many for any one person to investigate. An annotated selection of some of the more relevant appear here. If you have suggestions for other links, please send them, with annotations, to Alex. F. Burr.
There are a number of internet sites designed to answer physics and math questions from students and teachers, Some are listed below.
The Wikipedia is surprisingly good.
Good authoritative math info at all levels, including the highest, at Mathworld
Good answers to school questions by Dr. Math