Beall's Predatory Open Access Journal List
This librarian is Jeff Beall. He created Beall's list which is actually called "Potential, possible, or probable predatory scholarly open-access publishers." Librarians and authors consult it when evaluating journals, keeping in mind that he tends to put any journal, no matter how reputable or how sound their peer-review process, on this list if they charge their authors to publish (Gold Open Access). Compared to traditional publication models, Gold OA makes it easier for predatory publishers to exist, but not all Gold Open Access publishers are predatory. He also tends to judge a journals' origins negatively, if from a developing country. He posts his criteria for determining predatory journals on his page.
His list can be useful, if we understand that the journals he lists are only potentially or possibly predatory. We still have to evaluate each journal based on its own merit or lack of merit.