Once you've planned out your search strategy, you have to decide where to search! Sometimes good information on your topic is located in lots of places, but sometimes you have to be more picky.
If what you want to write about just happened or is a very new phenomenon... you'll probably want to start with newspapers, news sites, and careful open web searching, because not enough time has passed for much if any scholarly work to be done on the topic.
If what you want to write about is relatively new but not extremely so... you'll probably be able to find articles on the topic from newspapers, magazines, and scholarly journals. You can search for these sources in library databases and/or using Google Scholar.
If what you want to write about is an established research interest... you should be able to find a book or book chapter that deals with it, possibly including a bibliography to point to you to other sources, like journal articles. (Try SouthernSearch for all our ebooks in full text.)
If you are too unfamiliar with your topic to know how new it is... try to find out something about it from an encyclopedia or other reference work (also available in SouthernSearch under "Reference Entries"). This is where Wikipedia is both helpful and acceptable, especially for new phenomena that haven't made it into books yet!
For Interdisciplinary Studies in Particular
If you need to find varying perspectives on the same topic, it helps to use discipline-specific databases so you know that the information you're getting is relevant to whichever areas of knowledge you're working with.
Pay close attention to the language and focus points of each discipline. What seem to be areas of concern? This is the best way to narrow down a topic to a manageable research question.