DuckDuckGo - search engine
wikiHow - how to do anything...
Wikipedia - the free encyclopedia
Wolfram Alpha - computational intelligence
Python - a programming language that lets you work quickly
GlowScript - an easy-to-use, powerful environment for creating 3D animations and publishing them on the web
Trinket - an all-in-one coding environment designed for education
True BASIC - an easy to learn structured programming language
E&M applets - interactive Java tutorials
Lagrange points - five special points where a small mass can orbit in a constant pattern with two larger masses
The Physics Classroom - a variety of physics teacher resources

 Paul Falstad's applets - physics, engineering and math

ripple tank - large selection of sources