DOAJ (Directory of Open Access Journals) is the premier place to access open access peer-reviewed journals in all subjects.
The Social Science Research Network (SSRN) "is devoted to the rapid worldwide dissemination of social science research and is composed of a number of specialized research networks in each of the social sciences."
It includes both an abstracts database (over 345,000 items) and a collection of full text papers (280,000). SSRN Networks include free and fee-based journals in 13 subject areas ranging from accounting to rhetoric.
over 100 OA journals
... at Open J-Gate
SpringerOpen - read more here.
Hindawi Publishing specializes in STM journals
Learn more about participating High Energy Particle (HEP) physics journals and institutions in the SCOAP3 project.
New since 2011, GigaScience is an international journal published by BioMed Central. Co-published also by BGI Shenzhen (Beijing Genomics Institute: one of the world's largest data-producing and analysis centers), GigaScience produces articles relating to biological and biomedical "big-data" studies.
Metavid is a highly searchable database of videos of congressional proceedings from both houses of Congress spanning 2006 - present.
See the Prelinger Archives
About two-thirds of the films listed are available for free download via the Internet Archive.
Fifty educational and research institution partners have made their digital archives available in HathiTrust.
Visit the Digital Collections and Services gateway at the Library of Congress to locate digital photographs, sound recordings, manuscripts, books, maps, and other materials. Includes historical newspapers and veterans items too.
Explore digital collections around the world and investigate exciting opportunities for research in the Global Gateway at the Library of Congress. Includes also multimedia such as webcasts and selected videos.
links to a variety of open access books, including scholarly texts, trade books and creative works such as novels.
Google makes public data available through its Public Data search engine.
Search here for worldwide governmental population, demographic, employment, transportation, public health, economic, energy, education statistics, and more.
Visit USA.gov for a directory of all U.S. agencies by branch or topic.