Academy of Achievement - Famous people are divided into career categories for easy searching. Students can put in personal characteristics and the site will match them up to famous people with the same characteristics!
America's Story - Biographies of folks that were influential in making America what it is today. There are not as many bios here as other sites, however, the links included help tell America's story. This is a Library of Congress site and very well done.
Biographies for Kids - Bios of presidents for the younger readers. Each bio is accompanied by real pictures and fun activities at the end of the article. This site also shows the student how to cite the article.
Ducksters - This is a great biography site along with a ton of history! Wonderful resource for your social studies class for sure!!
SweetSearch - This site has thousands of biographies that are categorized by profession, country, ethnicity etc. When searching, you have the option to narrow your search several times to find just the person you are looking for.