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.
Videos and DVDs include both streaming online video and physical DVDs at the library. These are great sources for images, interviews, and (sometimes) statistics.
Articles can include news, scholarly (peer-reviewed) research, or data and analysis of your topic.
The best way to find articles is to use the same general databases you're familiar with from looking for scholarly articles (go to the Scholarly (Peer-Reviewed) Sources tab and use Academic Search Complete or ProQuest) but do NOT check the "Scholarly (peer-reviewed) Journals" check box to see all different article types.
This sample search of "green tea" in the image below found over 79,508 books, articles, videos.
(click on image to enlarge)