Mathematicians have been changing the history of the world since the Babylonians invented the abacus in the fourth century B.C. The following internet resources will help you bring to life the stories of famous mathematicians and math inventors for your class.
Start with the MacTutor History of Mathematics Archive. Here you'll find an overview of math history from 2000 B.C. to modern mathematical thinking. The site also includes a detailed chronology of math throughout history, as well as biographies of math pioneers and inventors.
You can also teach about the inventors who pioneered and perfected calculating machines. One such inventor was Ada Byron Lovelace, a pioneering female mathematician whose work was vital to Charles Babbage's development of the first "analytical engine" — the forerunner of the modern-day computer. You can read about Ada and other pioneering female mathematicians at the Women Mathematicians site, courtesy of Agnes Scott College.