Articles can include news, scholarly (peer-reviewed) research, or criticism / reviews / essays about your topic.
In order to locate criticism and commentary, look for articles that come from publications that include more complex, in-depth articles-- such as magazine features, academic criticism from (peer-reviewed) literary or pop culture journals, and review sources that publish longer essay pieces (New York Times Review of Books, etc.).
Videos and DVDs include both streaming online video and physical DVDs at the library. These are great sources for images, interviews, and (sometimes) statistics.
Books are a good source for connecting your topic to the "larger picture" by bringing in history or the social context (why your topic is important, etc.). You don't have to read the entire book to have it as a source-- you can use a smaller part of it if you like.
This sample search of "green tea" in the image below found over 79,508 books, articles, videos.
(click on image to enlarge)
