Georgia State University
Georgia State University: Hyper Physics: Kepler's Laws
An outstanding page describing Kepler's three laws of planetary motion.
Physics Classroom
The Physics Classroom: Circular and Satellite Motion: Kepler's Three Laws
Through interactive practice problems and examples, students explore Kepler's Three Laws of Planetary Motion.
Wolfram Research
Wolfram Math World: Cavalieri's Principle
This site gives brief information on Cavalieri's Principle.
Cornell University
Cornell University: Astronomy: Orbital Motion and Kepler's Laws
At this site from the Astronomy Department of Cornell University, Kepler's three laws of planetary motion are stated. There are brief explanations of each, along with links to additional information on related subjects.