Open access (OA) is free, immediate, permanent, full-text, online access, for any user, web-wide, to digital scientific and scholarly material, primarily research articles ...
http://en.wikipedia.org/wiki/Open_access

Categorized, searchable links to free, full text, quality controlled scientific and scholarly journals.
http://www.doaj.org/

UK Countryside Agency's portal on public use rights under the Countryside and Rights of Way Act of 2000.
http://www.openaccess.gov.uk/

PubMed Central (PMC) is a free digital archive of biomedical and life sciences journal literature. It is developed and managed by the National Center for Biotechnology Information ...
http://www.pubmedcentral.nih.gov/about/openaccess.html

Open access journals are scholarly journals that are available to the reader "without financial or other barrier other than access to the internet itself.
http://en.wikipedia.org/wiki/Open_access_journal