Adapted from CSULB Gray Literature Research guide located at http://www.csulb.edu/library/subj/gray_literature/
DOE's Scientific and Technical INFORMATION BRIDGE
"Full-text documents produced and made available by the Department of Energy National Laboratories and grantees from 1995" to date. Select Easy Search or Advanced Search.
lanl.arXiv.org ePrint archive
This is a huge "e-print service in the fields of physics, mathematics, non-linear science, computer science and quantitative biology maintained by Cornell University."
Networked Computer Science Technical Reference Library
NCSTRL is a database of full-text computer science technical reports, mostly from universities, and also from some research centers.
Virtual Technical Reports Center
A good place to start if you are looking for preprints and technical reports from around the world, by institution. This site lists hundreds of gray literature producing agencies.
Hewlett Packard Laboratories Technical Reports
This site has HP Labs technical reports from 1990 to the present. Topics include computer science, communication networks, and applied mathematics.
Jet Propulsion Laboratory Technical Report Server
JPL is the chief NASA center dedicated to planning, creating, and running unmanned space mission for the purpose of exploring the solar system.
NTRS: NASA Technical Reports Server
This server provides access to abstracts and citations of unclassified NASA technical reports, as well as NACA (NASA's predecessor) technical reports, arXiv Physics Eprint Server, BioMed Central, and the Energy Citation Database (OSTI). Also included is some open (i.e., non-gray) literature.
Energy Technology Data Exchange
Get the latest energy-related research from this site. Registration (free) is required. "Includes information on all environmental impact of energy production and use, including climate change; energy R&D; energy policy; nuclear, coal, hydrocarbon and renewable energy technologies and more." Search 3,3500,000 records and 160,000 full text documents.
Scientific and Technical Information Network
Use to search the public file for technical reports, from 1974 to the present. This will retrieve unclassified technical reports of interest to the defense community, from various sources. Some reports have full text online.
New York Academy of Medicine: Grey Literature
Use to find medical and health science related grey literature. Website includes a list of Grey Literature Producing Organizations and a quarterly Grey Literature Report with new resources.
Agricultural Online Access (Agricola)
"This database administrated by the National Agricultural Library and provides access to records of articles, chapters, reports, and reprints, encompassing all aspects of agriculture and allied disciplines."
US Army Corps of Engineers, Publications
"The only repository for all official USACE engineering regulations, circulars, manuals, and other documents".