Most items found in the library databases are not OER because they are licensed materials, they are materials that you can offer to your students at no additional cost to them.
Open access articles are not strictly OER since they can't be altered or remixed. However, they are a resource you can offer your students at no additional cost.
BioMed Central (http://www.biomedcentral.com/)
Directory of Open Access Journals (http://www.doaj.org/)
HighWire Free Online Full-text Articles (http://highwire.stanford.edu/lists/freeart.dtl)
Wiley Open Access (http://www.wileyopenaccess.com/view/journals.html)