Presidents of the United States - Archontology - A directory of American Presidents from 1774 to 2005 with dates of rule or office and selected biographies. Note that this includes Presidents of the continental Congress who served under the Articles of Confederation.
From the site:
Archontology - study of historical offices and office holders, including chronology, succession of rulers and governments, their biographies and other related records.
This web site was initiated in 1999 as the National Politics Web guide (former web address http://lego70.tripod.com), which existed until September 2004. Currently, Archontology.org is aimed at providing detailed archontological records for a number of selected nations.