When you find an article or book that is perfect for your research, pay attention to what is being cited in it. Most likely, those sources will also have good information for your research. When you find one great source, always browse the reference list and make note of the other sources that will also be a good fit for your research.
Follow the "scholarly conversation" via citation tracking and citation analysis.
Google Scholar Citation Count
Google Scholar allows you to use the Google search engine to look for scholarly articles instead of browsing the entire web. Look in the bottom left of each result to see the number of times the article has been cited by others.