Books and Writers features a profile of O. Henry, along with a bibliography and a list of books for further reading on the writer.
ClassicReader.com features a biography of O. Henry and has links to his short stories online.
An Exile in Paradise is an article by Raymond Lowry that describes the time William Sydney Porter spent in exile in Honduras.
The Literature Network has a biography of O. Henry and links to his short stories that let you read them online.
Lone Star Junction is a resource for Texas history and features a brief biography of O. Henry. The site also features the text of O. Henry's story, Last of the Troubadours.
"O. Henry." Authors and Artists for Young Adults, Volume 41. Gale Group, 2001. Reproduced in Biography Resource Center. Farmington Hills, MI.: The Gale Group, 2003. Document Number: K1603000795.
has a short, interesting article about O. Henry that gives insight into his life.
Selected Books about O. Henry (William Sydney Porter)
Authors & Artists for Young Adults, Volume 12. Detroit, MI: Gale, 1994.
Arnett, Ethel Stephens, O. Henry from Polecat Creek. Washington, D.C.: Piedmont Press, 1962.
Blansfield, Karen Charmaine, Cheap rooms and restless hearts: a study of formula in the urban tales of William Sydney Porter. Bowling Green, Ohio: Bowling Green State University Popular Press, 1988.
Current-Garcia, Eugene, O. Henry (William Sydney Porter). New York, NY: Twayne, 1965.
Langford, Gerald, Alias O. Henry: a biography of William Sidney Porter. Westport, Conn.: Greenwood Press, 1983, 1957.
O'Connor, Richard, O. Henry: The Legendary Life of William S. Porter. New York, NY: Doubleday, 1970.
Stuart, David, O. Henry: A Biography of William Sidney Porter. New York, NY: Stein & Day, 1987.