Eurostat. From the Statistical Office of the European Commission. Many publications, data sets, and tables available for free.
International Statistics. Links to all statistics programmes of the United Nations, of the United Nations Specialized Agencies (FAO, ILO, IMF, etc), and selected Autonomous Organizations (Eurostat, World Trade Organization, OECD, etc).
LABORSTA. Data on employment, unemployment, wages, labour cost, Consumer Price Indices, occupational injuries, strikes and lockouts, hours of work, etc. Covers over 200 countries or territories, some data going back several decades. From the Bureau of Statistics - International Labour Organization (ILO).
NationMaster. Country statistics from a variety of sources. Users can create graphs comparing countries on particular statistics.
OECD Statistics Portal. Provides data by topic, e.g. health, education/training, information, communication, energy, environment, finance, technology, social welfare, etc. From the Organization for Economic Cooperation and Development (OECD).
OFFSTATS. Links to official statistics. Searchable by country, region, topic.
Organization of American States (OAS). Describes organization, charter, structure, mission, member states. Includes publications, documents, webcasts.
Includes World Development Indicators, Global Development Finance, Education Statistics, Health Nutrition and Population Statistics, Africa Development Indicators, Global Economic Monitor and Millenium Development Goals.