This site provides an excellent summary of existing theories and models, including Behaviorist Theories, Cognitivist Theories, Constructivist, Social, and Situational Theories, and Motivational and Humanist Theories to name a few.
This website discusses examples of important psychological theories as related to the study of the human mind and behavior.
Research Methods Knowledge Base
This source examines the concept of a variable, providing types of variables along with examples.
University of Wisconsin
As related to the latter half of chapter 2, this site provides a discussion of logic models, along with a template and illustration of how to create one.