More Kepler, by Michael Fowler
Part two of a biography, discussing Kepler's investigations of planetary motion and gravity.
http://galileoandeinstein.physics.virginia.edu/1995/lectures/morekepl.html

Johannes Kepler
A short biography.
http://galileoandeinstein.physics.virginia.edu/1995/lectures/kepler.html

Tycho Brahe and Johannes Kepler
Short biographies.
http://galileoandeinstein.physics.virginia.edu/lectures/tycho.htm

Astronomy History - Johannes Kepler
Brief biography highlighting his status as a defender of Copernicus and a formulator of planetary-motion laws.
http://space.about.com/library/weekly/aa090702a.htm

Kepler, Johannes (1571-1630)
Encyclopedia entry provides a brief biography of this German astronomer and mathematician.
http://www.encyclopedia.com/html/k/kepler-j1.asp

Johannes Kepler
Includes detailed biography, online links, outlines of some of his works, quotes, and reading list.
http://www.johanneskepler.com

Starry Messenger: Johannes Kepler
Biography, and information on Kepler's mathematical techniques, poetry, and interest in astrology. From the Whipple Museum of the History of Science.
http://www.hps.cam.ac.uk/starry/kepler.html

Johannes Kepler and the Music of the Spheres
An article by David Plant describing Kepler's astrological beliefs.
http://www.panplanet.com/articles/davidplant.htm