Predatory journals exploit the open access movement by offering online content that has not been peer reviewed or edited up to standards. These journals trick scholars into paying to submit their publications, often by using fraudulent information and preying on the pressure for the scholar to publish.
Qualities of Predatory Journals:
Everything you ever wanted to know about predatory publishing but were afraid to ask. Monica Berger. Introduction to OA and Predatory Journals, including recent studies and detailed characteristics of Predatory journals.
No More 'Beall's List' Carl Straumsheim.
Who's afraid of Peer Review? John Bohannon. Article from 2013 describing the author's experience when he submitted several poorly research papers to suspicious open access journals.
Retraction Watch. Blog that lists recent retractions of scientific papers.