Virtual Reference Shelf
The Library of Congresses entry into the Reference wars. Also check out their Alcove 9 [http://lcweb.loc.gov/rr/main/alcove9/] "The Main Reading Room of the Library of Congress has eight alcoves. This ninth "virtual alcove" is a collection of websites selected and annotated by Humanities and Social Sciences Division subject specialists."
The link address is: http://www.loc.gov/rr/askalib/virtualref.html