These directories can be used to help discover OA publications:
These publishers give authors the option to pay a fee to make their article immediately open access, although the publisher still retains copyright. This hybrid model of open access does not always apply to the publisher's full suite of journals.
Many publishers hosted by HighWire Press offer free access to the back-files of biomedical journals.
Sherpa/RoMEO is a searchable database of publisher policies on the self-archiving of journal articles on the web and in Open Access repositories. The archiving rights policy for each publisher's entry is coded according to a colour category.
All open access journals allow archiving and can be taken as RoMEO "green". "Gold" is not a RoMEO colour category, but is often used to describe publishers of open access journals.