Grey literature includes research & technical reports, working papers, government documents, white papers and evaluations. This type of research is usually found for free, online and often contains important information that you might not find in the library.
"Science.gov is a gateway to U.S. government science information. The portal offers free access to research and development (R&D) results and scientific and technical information from scientific organizations across 13 federal agencies."
"WorldWideScience.org is a global science gateway comprised of national and international scientific databases and portals. WorldWideScience.org accelerates scientific discovery and progress by providing one-stop searching of databases from around the world."