Nasa (The Sci Fi Files)- Nasa's site is easy to use and is very helpful to learn about the science of action reaction forces, as well as the science of air resistance and other space related topics.

Wikipedia (English)- Wikipedia is very biographical and is useful if you are searching for information about Sir Isaac Newton.

Physics Classroom - The physics classroom is a very informational site that has practice problems to use to get to know Newton's laws and much more.