The Statistical Abstract of the United States is often the best place to begin when searching for data on nearly any topic pertaining to or within the US. It can be used to find data and it can be used as an index to identify sources of data to explore further. The link above will direct you to the Statistical Abstract series (discontinued after 2012).
Among other things, the ICPSR "maintains a data archive of more than 500,000 files of research in the social sciences. It hosts 16 specialized collections of data in education, aging, criminal justice, substance abuse, terrorism, and other fields." In many cases the files contain raw data that require a statistical tool for use.
Statista is a platform of data and statistics on media, business, finance, politics, and a wide variety of other areas of interest or markets. Statista gathers data from a wide variety of government and commercial sources and presents it in an easy to search interface. Data can be exported to Excel and charts can be exported as picture files or directly into PowerPoint. Data sources are categorized into industries, broad topics, countries, and digital markets.
Contains statistical data for over 800 development indicators and time series data from 1960, for over 200 countries and 18 country groups. Data include social, economic, financial, natural resources, and environmental indicators. Offers many useful features: results can be scaled, mapped, and charted; the mapping function allows users to see the results in a world map that can be resized and zoomed to the country level; data can be exported in standard formats such as Excel. 1960 to present.
Information is gathered by the Development Data Group of the World Bank. Information about their methods of data collection can be found here: http://go.worldbank.org/K2XOMZ5DC0