Anything which is written by scholars with the purpose of analyzing and correlating a past or historical event can be used as a secondary source.
The secondary source is the second, but very necessary, objective framework that dissects the information as it occurred, but still provides reliable and valid analysis of the event's beginning, middle, and end without adding personal bias.
This being said, you have several resources from which you can draw information--as long as the analysis included in the website is conducted within the parameters just discussed.
An example would be Oxford University Press online, particular, the Oxford Scholarship Online site. The link is provided in this answer. This webpage, an effort of Oxford University in England, refers to itself as a reliable resource for research that covers over 80,000 different entries in all academic areas. Each entry is written by a scholar who is an expert in the area, and has either researched the field personally or has written a textbook about on it.
Secondary data is information gathered for some other purpose than the one the researcher will be using it for. A census or other statistical survey would be an example of quantitative secondary research. Focus groups and field notes would serve as qualitative secondary research.
Here are some links to databases that hold secondary research content:
Though these types of resources save the researcher a lot of time and money gathering data themselves, and also might help a researcher to refine his or her orginal research topic by studying the available information and previous studies done about that topic, there are some disadvantages. For one thing, it is easy to skew the information or misinterpret it because the data wasn't originally collected for the researcher's particular purpose. It's very important to not only look at the research, but also at how it was conducted, who conducted it, and why. Context is essential in order to not generate faulty research. Another problem is that the data might not exactly answer the researcher's question, or the variables for the original study aren't as encompassing or exclusive as he or she would like. Finally, the flaws in the original study or any biases that were present might not be immediately apparent when viewing another person's research.
A good website to for social sciences is National Geographic. Of couse, here on enotes.com we have some study guides that are helpful for social sciences. Hope I helped!