T. Henderson, The Physics Classroom - An excellent tutorial on Newton's theory of gravity, including practice exercises.
Part of the Gravity: Making Waves bulletin from the American Museum of Natural History.
From The Physics Classroom site
Direct Measurement videos show situations that viewers can use to learn and apply physics concepts. Grids, rulers, and frame-counters are added as overlays on the video. These allow viewers to make precise measurements of quantities such as position and time.
I. Newton - A reproduction of the preface to Newton's famed Principia (1687) and links to the full text.
News & Events
The Cavendish Experiment was selected by physicists as one of the ten most beautiful experiments of all time.
News from around the world of science.
S. Smullin et. al., Stanford University - This research group is measuring the force of gravity on very-small-length scales and testing Newton's and Einstein's models of gravitation.
Google - Research database allows searching of the scholarly literature.
Paul A. Heckert, Ph.D. at Decoded Science