List Of Data Repositories (with APIs)

ARTstor
Biodiversity Heritage Library
Chronicling America Library of Congress National Digital Newspaper Program
Connecting Repositories (CORE)
Data Archiving and Networked Services (DANS)
Data-PASS
Digital Library for Earth System Education (DLESE)
Early Canadiana Online
English Broadside Ballad Archive (EBBA)
Europeana
FLOSSmole
Great War Primary Documents Archive
HathiTrust
History Data Service (HDS)
Infochimps.org
Inter-university Consortium for Political and Social Research
Internet Archive
Jisc MediaHub
JSTOR
Koninklijke Bibliotheek
Core.ac.uk

APIs
Chronicling America (Library Of Congress) - A digitized collection of American newspaper articles from the 18th to the 20th century.
Connecting Repositories (CORE) - A collection of open access articles from various sources hosted by the Open University.
English Broadside Ballad Archive (EBBA)
History Data Service (HDS) - A collection of data from a wide variety of historical sources.
Digging into Data API List