Institutional repositories
DSpace@MIT Massachusetts Institute for Technology
World Bank Open Knowledge Repository
Digital Access to Scholarship at Harvard
Discipline based repositories
arXiv e-Print archive. Open access to over a million e-prints in Physics, Mathematics, Computer Science, Quantitative Biology, Quantitative Finance and Statistics, now hosted at Cornell.
bioRxiv a preprint server for biology, operated by Cold Spring Harbor Laboratory.
Cogprints an electronic archive for self-archived papers in any area of Psychology, Neuroscience, and Linguistics, and many areas of Computer Science.
PubMed Central (PMC) is a free full-text archive of biomedical and life sciences journal literature at the U.S. National Institutes of Health's National Library of Medicine. Over 3 million articles.
Social Science Research Network "Social Science Research Network (SSRN) is a world wide collaborative of over 298,000 authors and more than 1.7 million users that is devoted to the rapid worldwide dissemination of social science research. Founded in 1994, it is composed of a number of specialized research networks in each of the social sciences. Each of SSRN's networks encourages the early distribution of research results by reviewing and distributing submitted abstracts and full text papers from scholars around the world." All scholars may submit papers for free, and author-submitted content is downloadable at no charge by users world-wide. (Bought by Elsevier in May 2016).
SocArXiv Open archive of the social sciences. Founded in spring 2016. About SocArXiv.
Directories of open access repositories
OpenDOAR A SHERPA service based at the University of Nottingham.
ROAR Registry of Open Access Repositories. A list of repositories maintained by Southampton University.
the Ranking Web of World Repositories from the Cybermetrics Lab of Spain's Consejo Superior de Investigaciones Científicas.
Simmons College list of discipline based repositories
The Open DOI resolver searches multiple repositories.
CORE Searches institutional repositories, subject-repositories and journal publishers worldwide. Very nice interface.
OpenDOAR Searches content in repositories worldwide.
OpenAIRE Searches content held in European repositories.
PubMed Central(PMC) a free archive of biomedical and life sciences journal literature, from the National Library of Medicine.
Europe PMC Great for searching the biomedical literature. Very user friendly interface. Includes U.S. Pubmed Central records in addition to European works.
OAIster A collaboration between the University of Michigan and OCLC. A union catalog of millions of records representing open access resources that was built by harvesting from open access collections worldwide using the Open Archives Initiative Protocol for Metadata Harvesting (OAI-PMH).
Digital Commons Network Search across repositories hosted on this Bepress platform. Includes CUNY's Academic Works.