The Creative Commons allows creators--authors, musicians, moviemakers--to provide more liberal rights to re-use their work than are provided in copyright law. It's a grassroots attempt to expand the public domain. OA Librarian operates under a Creative Commons license. While not every instance of a Creative Commons license provides complete open access, the Commons is a kindred spirit to the open access movement.
Google's advanced search mode allows you to search for content produced under various Creative Commons licenses. For the "Usage Rights" field, four search options correspond to various licenses: "free to use or share"; "free to use or share, even commercially"; "free to use share or modify"; and "free to use, share or modify, even commercially."
Further details about the Creative Commons license options are available here.