Has research on your topic already been conducted? When investigating your topic, think about many different words that could describe what you're looking for. One source may use different words from another source to describe your topic.
Example: if you want to research the impact of NGO spending and the impact on democracy in developing countries, there are number of different key words you might use to find information and a number of different places you might be able to find this kind of information. If you successfully find articles about your topic it is important to examine the bibliography of those papers very carefully. Did they use a dataset? If so which one? Has the dataset been updated since the paper was published?
The Data & Indexes page will provide you a list of various collections of data that you might use for research.
Search For Policy Reports from Think Tanks
U.S. Cabinet Level Agencies