Feynman Richard Phillips, and others.Feynman Lectures on Gravitation. Perseus, 1994, 2000. The principles of gravitation as taught by Feynman.
Gilbert, Harry, and Diana Gilbert Smith.Gravity, the Glue of the Universe. Teacher Ideas, 1997. Award-winning approach to a complex subject. For junior high and high school readers.
Narlikar, Jayant V.The Lighter Side of Gravity. W. H. Freeman, Cambridge University Press, 1982. 1996. A clear and nontechnical introduction to gravity in all of its manifestations.
Ohanian, Hans C., and Remo Ruffini.Gravitation and Spacetime. Norton, 1994. A fresh approach to general relativity.
Zee, Anthony.Einstein's Universe: Gravity at Work and Play. Oxford University Press, 2001. An animated discussion of Einstein's theory that succeeds in making complex ideas accessible.