Armed Conflict Location and Event Dataset (ACLED)

https://www.acleddata.com/

Geospatial data on macro and micro armed conflict trends and events

Center for Systemic Peace

http://www.systemicpeace.org/inscrdata.html

Maintains a number of datasets on conflict and governance, most famously the Polity 5 dataset on regime types. Also known as the INSCR Data Page 

Correlates of War (COW)

http://www.correlatesofwar.org/

Data on major conflicts (resulting in at least 1000 combatant deaths) from 1800 to the present. Includes datasets on international wars between states, civil wars within states, colonial wars between states and non-state entities, and wars between non-state entities.

Chicago Project on Security and Threats (CPOST)

https://cpost.uchicago.edu/

Dataset on suicide terrorism

Global Data on Events, Location, and Tone

http://www.gdeltproject.org/

A “global database of society”: a huge dataset of news and social media on almost any kind of event (violent, nonviolent, etc) from around the world. For advanced users only

Nonviolent and Violent Campaigns and Outcomes (NAVCO)

http://www.du.edu/korbel/sie/research/chenow_navco_data.html

Data on both nonviolent and violent campaigns, 1900-2011

National Consortium for the Study of Terrorism and Responses to Terrorism (START), Global Terrorism Database (GTD)

https://www.start.umd.edu/gtd/

A database covering terrorism events (successful or not) from 1970 to the present

Uppsala Conflict Data Program (UCDP)

http://ucdp.uu.se/downloads/

Hosts a number of datasets on armed conflicts after World War II, including specialized datasets on “one-sided” violence (massacres and genocides), as well as non-state conflicts, and geospatial data for use in GIS projects

Peace Research Institute Oslo (PRIO)

https://www.prio.org/Data/

Hosts and sponsors data, often in collaboration with UCDP and the Journal of Peace Research

Freedom House

https://freedomhouse.org/

A nongovernmental rights monitoring organization; ranks countries on a scale of 1-7 in terms of freedom

Polity IV

http://www.systemicpeace.org/polity/polity4.htm

One of the most widely used datasets on regime types, spanning a 20-point authoritarian-democratic spectrum

Varieties of Democracy (V-Dem)

https://www.v-dem.net/

A new research project aiming to create a more nuanced measurements of democracy, rights, freedom, and repression

Gap Minder

https://www.gapminder.org/

A project to present and visualize developmental statistics in new, compelling ways

United Nations Development Program (UNDP)

http://hdr.undp.org/

The annual Human Development Report publishes a “human development index” (HDI), along with the data that goes into the index, ranking all UN countries in terms of their progress along a number of indicators

World Bank

http://data.worldbank.org/

Good source for economic and other kinds of country-level data