For the most up-to-date listing of open-access journals, the Directory of Open Access Journals (DOAJ) site provides a directory of thousands of open-access journals.
For the most up-to-date listing of open-access books, the Directory of Open Access Books site provides a directory of thousands of open-access books.
The American Geosciences Institute (AGI) also provides a listing of open-access journals that GeoRef covers. Their listing only shows journals that appear to be stable, as well as a continual plan to remain open. Journals that require subscriptions to current issues are not included in their list.
The U.S. National Science Foundation's Public Access Initiative ensures the outputs of NSF-funded scientific research are made publicly available to the greatest extent, with the fewest constraints possible and consistent with law.
Visit NSF's public access initiative page for more information.