Statista: statistics portal: a general portal to a wide variety of statistical sources.

Social Explorer: Create custom tables and maps from the first Census to the latest Census, the American Community Survey, and the Religious Congregations and Membership Study. Social Explorer is THE "go to" source for access to Census data due to it's easy-to-use interface and download capabilities for more sophisticated analysis.

Data Planet (Statistical Datasets): Create customized tables and graphs using numeric data from a multitude of sources such as the Census Bureau, the Department of the Treasury, FDIC, the World Bank and China Data Center Online.

EIU Country Data and City Data
The City Data collection covers cost-of-living prices of products and services in cities worldwide. Performs data analysis and converts currency.  The Country Data collection contains annual, quarterly and monthly economic indicators and forecasts, covering more than 320 economic series for 150 countries, as well as 45 regional aggregates, running from 1980 and forecasting out five years.  When you click on the link above, scroll down the page to locate both collections - you access each separately.

Eurostat
Comprehensive statistical hub for European Union and candidate countries.  Use the Statistics tab to view available stats by subject.

MPI Immigration Data Hub
The Migration Policy Institute (MPI) Data Hub showcases the most current national and state-level demographic, social, and economic facts about immigrants to the US; as well as stock, flow, citizenship, net migration, and historical data for countries in Europe, North America, and Oceania.

OECD iLibrary
OECD iLibrary contains all the publications and datasets released by OECD (Organisation for Economic Cooperation and Development), International Energy Agency (IEA), Nuclear Energy Agency (NEA), OECD Development Centre, PISA (Programme for International Student Assessment), and International Transport Forum (ITF) since 1998.  Click on Statistics link at the top to go directly to the Statistics section. 

UNData
The United Nations Statistics Division (UNSD) of the Department of Economic and Social Affairs (DESA) launched an internet-based data service for the global user community. It brings UN statistical databases (including UNESCO, WHO, and UNAIDS) within easy reach of users through a single entry point where users can now search and download a variety of statistical resources.  You can manipulate data by the use of filters and pivot tables, and can download files in XML, comma, semicolon or pipe delimited.  Note that documentation is not included with much of the data, which can make interpretation of values difficult.  Also, data will not always be available for all countries, in all subjects, in all years.  The source of the data is always listed below your data table if the data are unclear.

World Bank Data
The World Bank's Open Data initiative is intended to provide all users with access to World Bank data. The data catalog is an expanding listing of available World Bank data sources.  Click on Data Catalog in the menu bar below the Data heading to see the full catalog and the ways in which you can access the data.  Please note that World Development Indicators is included here (direct link below for your convenience).

World Health Organization (WHO)
The WHO monitors the global health situation from mortality and burden of disease to health equity to road safety.  The Global Health Observatory is a deeper interactive database that brings together core health statistics for the 193 WHO Member States. It comprises more than 100 indicators, which can be accessed by way of a quick search, by major categories, or through user-defined tables. The data can be further filtered, tabulated, charted and downloaded.

Pew Research Center: The Pew Research Center is a nonpartisan "fact tank" that provides information on the issues, attitudes and trends shaping America and the world. It does not take positions on policy issues.  See "The Databank" menu or the "Projects of the Center" section to view statistics and download data.

Polling the Nations: A compilation of questions and responses from more than 12,000 national, state, local and special surveys, conducted by 700 polling organizations in the United States and 70 other countries from 1986 through the present. Each record in the database consists of one poll question and the participants answers. Only 4 simultaneous users can access Polling the Nations.

Roper Center for Public Opinion Research and iPOLL: Using iPOLL you can search for and view individual survey poll questions and answers.  There also is a ready list of "hot topics" that link to survey questions on current hotly debated/controversial issues.  Click on iPOLL link to begin your search.

Eurobarometer: Includes public opinion surveys and an interactive database by European Commission.