Freedom in World: This is a popular Freedom House data set that assigns each country a "freedom" value on a scale from 1 - 7.
Global Peace Index: The Global Peace Index ranks nations by their peacefulness. The Institute for Economics and Peace spearheaded this project.
Polity IV: This provides indices of political institutions such as level of democracy, state fragility etc.
Quality of Government Institute Standard: This dataset provides cross-national comparative data on quality of government indicators. Cross-sectional data pertaining to year 2002 and cross-sectional, time-series data spanning 1946 - 2009 are available.
Quality of Government Social Policy: This dataset provides cross-national comparative data on social policy indicators. Cross-sectional and cross-sectional, time-series datasets available.
Quality of Government Expert: This dataset contains dimensions of quality of government and is based on a survey of country experts.
KOF Index of Globalization: Data on the economic, social, and political dimensions of globalization since 1970, as well as subindices on economic flows, economic restrictions, information flows, personal contact, and cultural proximity.
CIRI Human Rights Index: One well-known human rights index that covers 195 countries from 1980-2010.
The SERF Human Rights Index: Index for how well countries fulfill economic and social rights
Corruption Index: One (of many) corruption indices covering approximately 100 countries, calculated as a latent variable that is directly related to its underlying causes.
3P Anti-Trafficking Policy Index: An index of governmental anti-trafficking efforts, in terms of prosecution of traffickers, prevention of human trafficking, and protection of victims, 2000-2010.
Archigos: A dataset of world political leaders 1875-2004, including information on manner of entry and exit, gender, and post-tenure fate.
Educational and Professional Background of Heads of Governments: Data on over 500 political leaders from 72 countries, 1970-2002.
Penn World Table: Purchasing power parity and national income accounts converted to international prices for 189 countries/territories, 1950-2009.
Correlates of War International Trade: Bilateral trade flows and total national exports/imports, 1870-2009.
Kristian Skrede Gleditsch Expanded Trade and GDP Data: data providing estimates of trade flows between independent states (1948-2000) and GDP per capita of independent states (1950-2000).
United Nations Commodity Trade Statistics Database (UN Comtrade): International trade statistics data provided to the UN Statistics Divison by 170 reporter countries.
Harvard's Guide to Inter-Governmental Financial Data
DHS: Demographic and Health Surveys provide data at the household and individual level on a number of measures concerning health outcomes, wealth, education, nutrition, women's empowerment etc. It is necessary to send in a short proposal for access to data and data should be released within a day or two.
Living Standards of Measurement Survey: This source provides country level household surveys.
Maddison: This is a popular source for long run GDP data and population data.
World Development Indicators: The world bank's repository of annual development indicators.
IMF Programs and World Bank Projects: yearly dummies for the existence of IMF programs and World Bank Projects in 160 countries, 1970-2008.
AidData: One of the best existing sources of data on international aid projects.
Bureau for Research and Economic Analysis of Development (BREAD): Lots of development data, including household surveys, firm level data, macro data, and links to national statistical offices.
Jameel Poverty Action Lab (J-PAL): Provides data from some high quality randomized controlled trials.
NGO Aid: Aid expenditures by 61 NGOs in 2005.
Sebastian Bauhoff: Collects links to useful development economics datasets.
ILO LABORSTA: labor data and metadata for over 200 countries or territories.
UN Treaty Collection: Source of treaties
United Nations Security Council Membership: A dataset containing a dummy variable indicating if a country has been a temporary UNSC member in a given year.
United Nations General Assembly Voting: Country voting behavior, 1946-2008.
International Courts Data: On compliance, judicial dissents, biographical information on judges, case-law citations, background information on judgments, sentencing by criminal courts, reservations made by states to the jurisdiction of courts, etc.
World Treaty Index: electronic treaty database spanning the 20th century.
The Alliance Treaty Obligations and Provisions (ATOP): data regarding the content of military alliance agreements signed by all countries of the world between 1815 and 2003.
Paul Hensel's International Relations Data Site: data on international affairs/cooperation, economics, environment, politics and social issues.
SEDAC Environmental Sustainability: This provides national level data on environmental performance, sustainability and vulnerability
Collection of Environmental Data: Lots of data on different aspects of the environment, mostly for environmental economics.
Correlates of War Militarized Interstate Disputes: Threats, displays, and the use of force between states, 1816-2006.
Correlates of War National Material Capabilities: a composite index of national capability, plus data on total population, urban population, iron and steel production, energy consumption, military personnel, and military expenditure, 1816-2001.
Issue Correlates of War Territorial, River, Maritime, and Regime Claims: Data covering 1816-2001.
Issue Correlates of War Colonial History: Data covering 1816-2001.
Ten Million International Dyadic Events: Day level international relations events covering 1990-2004.
Penn State Event Data (Formerly Kansas Event Data): Regional day level event datasets covering the Levant, Turkey, the Gulf, Central Asia, the Balkans, West Africa, and mediation in the Levant and Balkans, various years.
UCDP/PRIO Armed Conflict Dataset: A conflict-year dataset on armed conflict where at least one party is the government of a state, covering 1946-2010.
UCDP Conflict Data: Various datasets on georeferenced events, external support, actors, conflict termination, peace agreements, one-sided violence, battle-related deaths, and low-intensity conflict.
Armed Conflict Location and Event Data: Data on political violence in developing states, with the dates, location, and types of violence, as well as the groups involved.
Small Arms Trade: Covering 250 states and territories over 1962-2007.
Political Instability Task Force Worldwide Atrocities Dataset: Data on the deliberate killing of noncombatant civilians in political conflicts, 1995-2011, geocoded and standard.
Minorities at Risk: Data on the status and conflicts of all politically active communal groups with populations totaling at least 500,000.
Global Terrorism Database: Day-level domestic and transnational terrorist events categorized by type, target, and perpetrator, 1970-2010.
International Terrorism: Attributes of Terrorist Events (ITERATE): Day-level data on transnational terrorist events, 1968-2010.
Peace Science Society: A resource for data on peace analysis and conflict management, but also welcomes and utilizes relevant work on the social and natural sciences. The primary concern of PSS is the improvement of social science theory as it relates to internation relations.