Federal Employment Viewpoint Survey
The Federal Employee Viewpoint Survey (FEVS) is a tool that measures employees' perceptions of whether, and to what extent, conditions characterizing successful organizations are present in their agencies. Survey results provide valuable insight into the challenges agency leaders face in ensuring the Federal Government has an effective civilian workforce and how well they are responding. Survey reports from 2004 to 2015 are available online.

Federal Election Commission
The data available for download from this page range from zip files that contain individual contributions to political committees and may exceed 100 megabytes to single page summary pdf and xls files. While the largest files may be of interest primarily to campaign finance professionals there is much information here that could be useful for anyone trying to understand how money is raised and spent for the purpose of influencing federal elections.

Yearbook of Immigration Statistics, Homeland Security
The Yearbook of Immigration Statistics is a compendium of tables that provides data on foreign nationals who, during a fiscal year, were granted lawful permanent residence (i.e., admitted as immigrants or became legal permanent residents), were admitted into the United States on a temporary basis (e.g., tourists, students, or workers), applied for asylum or refugee status, or were naturalized. 

Medicare Provider Utilization and Payment Data, Centers for Medicare & Medicare Services
Data are being released that summarize the utilization and payments for procedures, services, and prescription drugs provided to Medicare beneficiaries by specific inpatient and outpatient hospitals, physicians, and other suppliers. These data include information for the 100 most common inpatient services, 30 common outpatient services, all physician and other supplier procedures and services, and all Part D prescriptions.

The National Institute of Standards and Technology (NIST) Dataset
The National Institute of Standards and Technology (NIST) has compiled and released a comprehensive set of data detailing federal technology transfer activities between 1987 and 2009. This report compiles in a single place data from multiple sources.  By releasing the raw, unanalyzed data, NIST aims to further ongoing research to improve the measurement and evaluation of federal technology transfer efforts and, ultimately, to broaden their impact.

Civil Rights Data Collection (CRDC), the U.S. Department of Education
The U.S. Department of Education [ED] conducts the Civil Rights Data Collection (CRDC), formerly the Elementary and Secondary School Survey (E&S Survey), to collect data on key education and civil rights issues in our nation's public schools. The CRDC collects a variety of information including, student enrollment and educational programs and services, disaggregated by race/ethnicity, sex, limited English proficiency and disability.

Office of Federal Financial Management Improper Payments Dataset
This dataset contains information on improper payment measurements, from FY 2004-FY2011, for programs found to be susceptible to significant improper payments under the Improper Payments Information Act, as amended by the Improper Payments Elimination and Recovery Act. 

Data.Hud.gov
As a priority Open Government Initiative for President Obama's administration, DATA.HUD.GOV increases the ability of the public to easily find, download, and use datasets that are generated and held by the U.S. Department of Housing and Urban Development. DATA.HUD.GOV provides descriptions of HUD's datasets (metadata), information about how to access the datasets, and tools that leverage government datasets. The data catalogs will continue to grow as datasets are added.

OMB Data Inventory
As called for in the Open Government Directive, this list of datasets inventories OMB high-value information currently available for download, or provides dates for when the information will be available.

Data.Medicare.gov
This site provides direct access to the official data from the Centers for Medicare & Medicaid Services (CMS) that’s used on the Medicare.gov Compare Websites and Directories. The goal of the site is to make these CMS data readily available in open, accessible, and machine-readable formats.

Federal Health Data
This site is dedicated to making high value health data more accessible to entrepreneurs, researchers, and policy makers in the hopes of better health outcomes for all.

Data, Analysis & Documentation, Office of Personnel Management, U.S.
OPM issues government-wide guidance on documentation of Federal employment. In addition, OPM issues guidance on reporting human resources, payroll and training data which are based on instructions of government-wide data element standardization and system edits.

Central Intelligence Agency

Office of Management and Budget
This site contains the most recent U.S. federal budget.  There are also historical tables regarding specific components of the budget and supplemental materials discussing specific budget assumptions.  Past budgets can be found at the U.S. Government Printing Office

U.S. Census of Government
Taken every 5 years, the Census of Government provides detailed lists of governmental bodies in the U.S., their structure, employment and payrolls, and financial characteristics.  There are also annual surveys of governmental revenues.  These are supplemented by quarterly surveys of state and local revenues, and annual surveys of federal, state, and local finances, as well information for public school districts.

Open Data in the United States
Since his first full day in office, President Obama has prioritized making government more open and accountable and has taken substantial steps to increase citizen participation, collaboration, and transparency in government.