Note: the list has now gone 'dark' (see comment below).
Access last published versions via this resource.
This website, maintained by University of Colorado Librarian Jeff Beall, is a platform for the critical analysis of scholarly open access publishing [sub-title to the main website title].
The principal purpose of the website is to host Beall's List of "potential, possible, or probable predatory scholarly open-access publishers". Predatory publishers and journals are those where editorial standards such as peer review are highly compromised, with the main aim being to secure authors' publication fees. The website provides a separate list of standalone journals suspected of similar practices. It is important to note that this second resource is not a comprehensive list of potentially predatory journals, only those that are standalone: the first place to check would be the list of predatory publishers. Both the lists are impressively long.
The blog discussions are illuminating.