According to Wikipedia, "self-archiving, also known as green open access, refers to the practice of depositing articles in an open access repository, this can be an institutional or a disciplinary repository such as arXiv." Typically, researchers archive pre- or post-print versions of a journal article so that those without a subscription to the journal can still have access to the article. Not all publishers allow this, but the practice is increasingly common and is a good way to foster accessibility even if you choose not to publish in an OA journal.
Photo credit: Delde Open Access Journals
Many publishers now allow some form of archiving locally (see SHERPA/RoMEO). This means that authors can deposit their work voluntarily in repositories at their own institutions or funding agencies, or a disciplinary repository. Sometimes the publisher's version of the PDF may be included in a repository, but commonly authors need to contribute their final, peer-reviewed version of the article.
Iowa Research Online, UI's institutional repository, was created to organize, preserve, and increase the impact of scholarly and creative work at The University of Iowa. It is a dynamic archive of the research produced by faculty, researchers, and students, from published articles in peer-reviewed journals to presentations, theses, dissertations, and unpublished papers. Many institutions all over the world have repositories.
Green Open Access encourages researchers to archive their work, either in their institution's repository or in a repository specific to a certain academic discipline. Examples of disciplinary repositories include:
Open access to over 500,000 e-prints in Physics, Mathematics, Computer Science, Quantitative Biology, Quantitative Finance and Statistics. Hosted by Cornell University Library.
PMC is the U.S. National Institutes of Health (NIH) free digital archive of biomedical and life sciences journal literature. All research funded by the NIH now goes into PMC, with a maximum embargo period of 12 months.
AgEcon Search collects, indexes, and electronically distributes full text copies of scholarly research in the broadly defined field of agricultural economics including sub disciplines such as agribusiness, food supply, natural resource economics, environmental economics, policy issues, agricultural trade, and economic development. Maintained at the University of Minnesota by Magrath Library and the Department of Applied Economic.
RePEc Research Papers in Economics
REPEc is a collaborative effort of hundreds of volunteers in 63 countries to enhance the dissemination of research in economics. The heart of the project is a decentralized database of working papers, journal articles and software components. All RePEc material is freely available.
Social Science Research Network (SSRN)
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.
History Data Service
The History Data Service collects, preserves, and promotes the use of digital resources, which result from or support historical research, learning and teaching. From the University of Essex.
OLAC (Open Language Archives Community)
OLAC is an international partnership of institutions and individuals who are creating a worldwide virtual library of language resources by: (i) developing consensus on best current practice for the digital archiving of language resources, and (ii) developing a network of interoperating repositories and services for housing and accessing such resources.
Oxford Text Archive
The Oxford Text Archive develops, collects, catalogues and preserves electronic literary and linguistic resources. From Oxford University.