General Sources

• Constituency-Level Elections (CLE) Dataset (1944-2007)
  
• Correlates of War (COW)
• Country Indicators for Foreign Policy (CIFP)
  
• Economic and Social Data Service (ESDS, Other longitudinal resources)
• Davidson Data Center & Network (DDCN)
• Harvard-MIT Data Center (HMDC)
• IADB DataGov - Governance Indicators Database
  
• ICPSR data
• Institute for Democracy and Electoral Assistance (IDEA)
  
• Lijphart Elections Archive (1980-2003)
• PARLINE Database on National Parliaments
• The World Business Environment Survey (WBES) Interactive Dataset
• Worldwide Governance Indicators (1996-2008)
  

Sources on Latin American countries

• CEPALSTAT (1990-2006)
• Observatorio de Elites Parlamentarias (ELITES)
• Observatorio Electoral Latinoamericano
• Oxford Latin American Economy History Database (OxLAD), 1900-2000
• Political Database of the Americas (Georgetown University)
  

Sources on International Relations

• The III-Treatment and Torture (ITT) project: Beta data and User's Guide 
• The World Treaty Index (1900-1999).  Extended Rohn's World Treaty Index, maintained by M. Bommarito, D.M. Katz and P. Poast

Lists of sources

• Sources for Democratic Governance Indicators (United Nations Development Programme)