Dictionaries, handbooks, and encyclopedias are a good starting place for psychology research, especially if you're not sure where to begin or overwhelmed by the choices. These resources can provide a scholarly summary of a particular subtopic in psychology; the terminology, names, and important works in that area (it's basically the academic version of browsing Wikipedia). By choosing a topic from one of these resources, you can be sure there is a sufficient pool of research to draw from for your project.
If you're unsure of where to begin, try searching for topics that interest you in the APA Dictionary of Psychology (below).
The DSM-5 Library is a series of ebooks that aid health professionals and legal specialists etc... in diagnosing and classifying mental disorders. The criteria are concise and explicit, intended to facilitate an objective assessment of symptom presentations in a variety of clinical settings- inpatient, outpatient, partial hospital, consultation-liaison, clinical, private practice and primary care.