C-SPAN - Life PortraitsThe Peabody Award-winning series profiles the men who have served as chief executive of the United States. This website, created as a companion to C-SPAN's 20th anniversary television series, provides an in-depth look at each of the presidents, their lives, families and administrations.
The Presidency - Miller Center / UVA"The Miller Center is a nonpartisan affiliate of the University of Virginia that specializes in presidential scholarship, public policy, and political history and strives to apply the lessons of history and civil discourse to the nation's most pressing contemporary governance challenges."
Library of Congress Digital Resources"The digital collections of the Library of Congress contain a large selection of primary source materials associated with the presidents of the United States, including manuscripts, letters, broadsides, government documents, prints, photographs, sheet music, sound recordings, and films."
NOTE: documents are only listed through Gerald Ford / 1977. HOWEVER, the material available is high quality and primary.
Presidents USA"owned and operated by Baaron's Hill, LLC, an independent entity not affliated with any government agency, university, or business. The goal of PresidentsUSA.net, which was first published in 2000 and assumed its current domain name in 2002, is to provide researchers, students, teachers, politicians, journalists, and citizens a complete resource guide to the United States Presidents and the Presidency."
Ad supported. Unclear who or what "Baaron's HIll, LLC" is.
POTUS.comBasic information and links about the Presidents. Seems to be a continuation of the now-defunct "Internet Public Library" site, compiled/edited by Robert S. Summers.