http://www.census.gov/acs/www/ -- American Community Survey (ACS) is an ongoing survey that provides data every year -- giving communities the current information they need to plan investments and services. Information from the survey generates data that help determine how more than $400 billion in federal and state funds are distributed each year.
http://www.census.gov/compendia/statab/-- Statistical Abstract of the United States, published since 1878, is the authoritative and comprehensive summary of statistics on the social, political, and economic organization of the United States.
http://www.census.gov/econ/ --Economic Census
http://electionstudies.org/ -- American National Election Studies (ANES) data enable researchers to better understand the theoretical and empirical foundations of national election outcomes.
http://dvn.iq.harvard.edu/dvn/ -- The Dataverse Network at the Institute for Quantitative Social Science at Harvard hosts data on social science research from all over the world.
http://www.fedstats.gov/ -- FEDSTATS handy finding aid for over 70 agencies in the United States Federal Government linked by topic.
http://www.gaportal.org/global-indicators/political-constraint-index -- Measure the feasibility of change in policy given the structure of a nation’s political institutions and the preference of the actors that inhabit them.
http://www.google.com/publicdata -- Makes large datasets easy to explore, visualize and communicate. As the charts and maps animate over time, the changes in th world become easier to understand. You don't have to be a data expert to navigate.
http://www.gpo.gov/fdsys/browse/collectionGPO.action?collectionCode=BUDGET -- Budget of the United States
http://ksdc.louisville.edu/ -- Kentucky State Data Center
http://www3.norc.org/GSS+Website -- GSS contains a standard 'core' of demographic, behavioral, and attitudinal questions, plus topics of special interest. Many of the core questions have remained unchanged since 1972 to facilitate time-trend studies as well as replication of earlier findings. The GSS takes the pulse of America, and is a unique and valuable resource. It has tracked the opinions of Americans over the last four decades.
http://www.oecd-ilibrary.org/statistics -- Organisation for Economic Cooperation and Development iLibrary is global knowledge base for OECP's data and analysis.
http://www.people-press.org/ -- The Pew Research Center for the People & the Press is an independent, non-partisan public opinion research organization that studies attitudes toward politics, the press and public policy issues. In this role it serves as a valuable information resource for political leaders, journalists, scholars and citizens.
http://www.policyagendas.org -- The Policy Agendas Project collects and organizes data from various archived sources to trace changes in the national policy agenda and public policy outcomes since the Second World War.
http://www.qog.pol.gu.se/data/ -- The QoG, Quality of Government, Institute offers a range of datasets on indicators of Quality of Government and all things related.
http://www.ssrn.com/ -- Social Science Research Network (SSRN) is an open access repository and devoted to the rapid worldwide dissemination of social science research.