Lots of valuable information about presidents and first ladies, too! http://www.whitehouse.gov/history/presidents/
The Internet Public Library Biographies, facts, links to other sites...and much more! http://www.ipl.org/div/potus
Great reference site with plenty of links to little known facts! http://www.kidinfo.com/American_History/Presidents.html
Site put together by C-Span. Biographies, key events, and some great "Did you know" facts. http://www.americanpresidents.org
Information on presidents from 1901 to the present. http://www.pbs.org/wgbh/amex/presidents/
If you still haven't found what you're looking for, try this site! http://www.whitehouse.gov/kids/presidents/