Grey literature may be very important for a number of topics; these are articles, reports, etc. from various organizations, individuals, etc. that are not the typical "peer-reviewed" literature. However, this literature is oftentimes extremely well researched & cited (although again, it will be difficult to locate the "paper trail" for these works). To the right, you will find some recommended places to start for this literature. One author caveat involves working papers or conference papers. It is usually best to determine first whether these papers have been published before using the working/conference paper version, since these are usually "drafts" of a more revised article.
There are numerous public policy institutes and research programs across the country that provide insightful analysis of numerous public policy/affairs issues. A few are highlighted here.
For international relations and foreign affairs, first check out CIAO--clunky interface, but good content.