Astronomy History - Johannes Kepler - http://space.about.com/library/weekly/aa090702a.htm Brief biography highlighting his status as a defender of Copernicus and a formulator of planetary-motion laws.
Starry Messenger: Johannes Kepler - http://www.hps.cam.ac.uk/starry/kepler.html Biography, and information on Kepler's mathematical techniques, poetry, and interest in astrology. From the Whipple Museum of the History of Science.
Johannes Kepler - http://galileoandeinstein.physics.virginia.edu/1995/lectures/kepler.html A short biography.
More Kepler, by Michael Fowler - http://galileoandeinstein.physics.virginia.edu/1995/lectures/morekepl.html Part two of a biography, discussing Kepler's investigations of planetary motion and gravity.