Open Access and Scholarly Communications: Finding OA Content

• arXiv 

  arXiv is a repository of electronic preprints, or e-prints, in the fields of physics, mathematics, computer science, quantitative biology, quantitative finance, and statistics.
• Google Scholar

  Google Scholar is a free search engine that allows you to search for scholarly content across multiple disciplines, formats, and sources
• Social Science Research Network (SSRN)

  Social Science Research Network (SSRN) is an open access repository of abstracts and full text papers by social science researchers from across the world. 
• PubMed

  PubMed is a free resource that includes over 24 million citations for biomedical literature from MEDLINE, life science journals, and online books. Coverage includes the fields of biomedicine and health, portions of the life sciences, behavioral sciences, chemical sciences, and bioengineering.
• Directory of Open Access Journals (DOAJ)

  DOAJ is an online directory that indexes and provides access to quality open access, peer-reviewed journals.
• OAIster

  OAIster is a union catalog of over 30 million records representing open access resources from collections worldwide.
• Bielefield Academic Search Engine (BASE)

  BASE is a freely available search engine for academic open access resources on the web. 

• Digital Public Library of America (DPLA)

  The Digital Public Library of America brings together the riches of America’s libraries, archives, and museums, and makes them freely available to the world.
• Directory of Open Access Books (DOAB)

  The DOAB is a searchable index of academic, peer-reviewed, open access books that includes links to the full-text books on the publishers' websites.
• HathiTrust

  HathiTrust is a partnership of academic and research institutions, offering a collection of millions of titles digitized from libraries around the world.
• OAPEN

  The OAPEN Library contains freely accessible academic books, mainly in the area of Humanities and Social Sciences. 

Images, Audio, Video and Other Media

• Search.CreativeCommons.org
• Wikimedia Commons
• flickr

Open Educational Resources

• OER Commons
• Open Education Consortium
• Open Textbook Library

Open Data

• Open Access Directory's list of data repositories