Adams, Alexander B. The Eternal Quest: The Story of the Great Naturalists. New York: Putnam, 1969. This book gives a separate chapter to each of the earlier naturalists or field explorers and scientists whom Darwin read before he set out on his voyage. It is entertaining written as a series of little lives.
Bowler, Peter J. Charles Darwin: The Man and His Influence. Cambridge: At the University Press, 1990. This book is valuable as one in which a modern scientist evaluates Darwin's contributions to geology, biology, and various areas of science all interwoven into a lucidly written story of Darwin's life with a thorough-going section on the five years Darwin spent on the Beagle.
Darwin, Charles. The Autobiography, ed. Nora Barlow. New York: Norton, 1958.
--------------------. Darwin: A Norton Critical Edition, ed., sel. Philip Appleman. 2nd Ed. London: W. W. Norton, 1979. This includes important sections of Darwin's On the Origin of Species, Teh Descent of Man, as well as many essays on his science and writing in the context of the Victorian era and our own.
Desmond, Adrian and James Moore. Darwin: The Life of a Tormented Evolutionist. New York: Norton, 1991. This is the best biography in print in paperback; it emphasizes Darwin the man. It is pleasurable reading.*
Alvar Ellegard. Darwin and the General Reader: The Reception of Darwin's Theory of Evolution in the British Periodical Press, 1859-1872. Chicago: Univ of of Chicago Press, 1990.
Ernst Mayr. One Long Argument: Charles Darwin and the Genesis of Modern Evolutionary Thought. Boston: Harvard Univ Pr, 1991. (An award-winner in science, solid yet very accessible.)
Farrington, Bejamin. What Darwin Really Said. New York: Schocken, 1966.
Gruber, Howard E. Darwin On Man: A Psychological Study of Scientific Creativity. Chicago: University of Chicago Press, 1981.
Hopkins, Robert S. Darwin's South America. New York: John Day, 1969. This book takes as its topic the South American Darwin visited; he tells something of the history, politics, war, and cultural milieu Darwin was passing through.
Irvine, William. Apes, Angels and Victorians: The Story of Darwin, Huxley, and Evolution. New York: McGraw-Hill, 1955. This lively book tells the story of Darwin in the context of his religious opponents from his own time to the early 20th century.
Moorehead, Alan. Darwin and the Beagle. New York: Harper and Row, 1969. This book is entertaining and instructive. It is filled with pictures and information of all sorts about Darwin's voyage. It is a sensible beginner's book which focuses on the story of the Beagle. *
Ralling, Christopher. The Voyage of Charles Darwin. New York: Mayflower, 1979. This shows how Darwin's put his journal together. Ralling provides information about all the notebooks Darwin kept (what they were meant for, how used, what's in them).
White, Michael and John R. Gribbin. Darwin: A Life in Science. New York: Penguin 1995. This is an excellent analysis of Darwin's achievement as a scientist.