The U.S. Census Bureau conducts demographic, economic, and geographic studies of other countries and strengthens statistical development around the world through technical assistance, training, and software products. For over 60 years, the Census Bureau has performed international analytical work and assisted in the collection, processing, analysis, dissemination, and use of statistics with counterpart governments in over 100 countries.

If you are working with an non-U.S. city, check this list of international statistical agencies to see there's one for your country.
To translate non-English web pages, look for a British or U.S. flag icon on the page.

Searchable data from the UN. A very simple interface, but it can be tricky to find information from this source.

Statistics from around the world on topics such as literacy, science, education, etc. From a branch of the United Nations.

From Northwestern University. Includes topics such as crime, economics, education, employment, trade, environment, health...etc.

"OECD iLibrary is the online library of the Organisation for Economic Cooperation and Development (OECD) featuring its books, papers and statistics and is the gateway to OECD's analysis and data."

Statistics by topic and country, including world development indicators