Archimedes, The Sand Reckoner, at http://web.fccj.org/~ethall/archmede/sandreck.htm .
Benson, Donald C., The Moment of Proof : Mathematical Epiphanies, Oxford University Press, 1999.
Dunham, William, Journey through Genius: Great Theorems of Mathematics, John Wiley & Sons, 1990.
Dunham, William, The Mathematical Universe : An Alphabetical Journey Through the Great Proofs, Problems and Personalities, John Wiley & Sons, 1997.
Ferris, Timothy, Coming of Age in the Milky Way, Anchor Books, 1989.
Ifrah, Georges, The Universal History of Numbers : From Prehistory to the Invention of the Computer, John Wiley & Sons, 1999.
Plutarch, Parallel Lives: Marcellus, at http://classics.mit.edu/Plutarch/marcellu.html
Stein, Sherman, Archimedes : What Did He Do Beside Cry Eureka?, Mathematical Assn of America, 1999.
The Drexel University web site, Archimedes, at http://www.mcs.drexel.edu/~crorres/Archimedes/contents.html
(I made liberal use of the resources at this excellent site).
Ilan Vardi's web site, The Legacy of Archimedes, at http://www.ihes.fr/~ilan/archimedes.html .
The University of St. Andrews web site, Archimedes of Syracuse, at
http://www-groups.dcs.st-and.ac.uk:80/~history/Mathematicians/Archimedes.html
.