One-stop resource for data on infectious diseases (over 2,000 pathogens). Provides information on diseases: history of outbreaks back to 1348AD, geographic spread, and treatment. Includes a visualization tool to create charts as well as a differential diagnosis tool. Information updated daily to provide the most current information.
The database has over 2.1 million full-text dissertations and theses. It also contains indexing of 3.8 million graduate works. Primarily US, UK and Ireland but increasingly from other countries. Designated as an official offsite repository for the U.S. Library of Congress. Coverage: 1861-present.
Thousands of test instruments (including aptitude tests, personality scales and cognitive functioning measures, surveys and other assessments), as well as descriptive information about tests that were developed for research but not made commercially available (i.e. unpublished tests).
50% of entries contain the actual test. Produced by the American Psychological Association (APA). Coverage: 1910-present.
Think tanks are institutions that generate public policy research, analysis and activity. Their output can include publications, reports, blogposts and journals. They can be independent or affiliated with other organizations. Most are non-profit, but some are funded by governments, advocacy groups, or corporations, and may derive revenue from consulting or research work related to their projects. They can be non-partisan or partisan, so pay attention to the goals of the organization when using the information they generate. You may also want to read the Wiki entry for each think tank to get an outsider's perspective on their goals.
Note that some public policy reasearch (often considered "grey literature") is indexed in the PAIS public policy database.
Harvard's Kennedy School Library has a website with useful information on evaluating think tanks and their research. They have also created a custom Google Search of over 1200 think tanks: