Sherpa/Romeo shows the open access permissions and restrictions for each journal covered with links to the publishers' copyright agreements.
Publishers are divided into categories depending on the self-archiving restrictions.
Examples of some publishers in science and engineering that are currently designated "white" (archiving not formally supported) by the Sherpa/Romeo Website (subject to change):
American Dental Association
Society for General Microbiology
Soil Science Society of America
Green designates publishers with the least restrictions, not all of which allow the posting or deposition of the publisher's PDF version. For manuscripts with considerable equations, tables, figures, etc. this can be a major handicap. Examples of publishers with this restriction are (subject to change):
American Society of Plant Biologists
John Wiley and Sons
You may also want to check out Beall's List of Predatory Open Access Publishers, a watchlist of publishers considered to be exploiting the OA Publishing process for their own profits at the authors expense.