General
Congress.gov has grown since it’s beta release in Fall 2012 through a collaborative effort between the Library of Congress, U.S. Senate, U.S. Representatives, and Government Printing Office (GPO). The new site includes bill status, texts and summaries, direct links from bills to cost estimates from the Congressional Budget Office, Congressional Record, committee reports, legislative process videos and committee profile pages going as far back as the 103rd Congress.
Think Tanks/Policy Centers
In addition to publishing journal articles and research reports, more and more researchers and government agencies are sharing the data they gather in their research. There is no central database or search engine for data sets, and data sets are not available on every topic. That said, you may be able to find one which enhances your research. Here are some examples:
Centers for Disease Control (CDC), Wonder: http://wonder.cdc.gov/datasets.html
Consortium of European Social Science Data Archives: http://www.cessda.org/
Housing and Urban Development, HUD User Data Sets: https://www.huduser.gov/portal/pdrdatas_landing.html
Integrated Postsecondary Education Data System: http://nces.ed.gov/ipeds/
Inter-University Consortium for Political and Social Research: http://www.icpsr.umich.edu/
Minnesota Population Center, MPC Data Projects: https://ipums.org/
National Bureau of Economic Research, Data: http://www.nber.org/data/
Pew Research Center for the People & the Press, Datasets: https://www.pewresearch.org/datasets/
World Bank, Research Datasets: https://databank.worldbank.org/