Non-governmental organizations are generally non-profit groups not affiliated with any government operating locally, nationally, and/or internationally.
NGOs often publish reports and statistics, which are available for free on their web sites, that may be of interest to researchers.
These groups vary widely in their goals and structures, but most have the objective of influencing public policy. Be sure to take this into consideration when evaluating their material.
Sites were chosen based on their consultative status with the United Nations Economic and Social Council (ECOSOC) and also collated from University of Minnesota Human Rights Library, Duke University Libraries' NGO Research Guide, and the World Association of Non-Governmental Organizations (WANGO). More background on the IGO/NGO search projects can be found at http://wikis.ala.org/godort/index.php/IGO_search including a growing spreadsheet of NGOs included in this search.