European Elections Database (EED)
The EED, which is hosted by Norwegian Social Science Data Services, "publishes regional election results according to the Nomenclature of Territorial Units for Statistics (NUTS), level 1 to 3" for a selection of 35 European countries for 1990 onwards. Data are available for parliamentary, presidential, and European Parliament elections.
Eurostat is the statistical office of the European Union. Eurostat collects statistical information from the member states of the EU, and its databases constitute a very comprehensive source for economic and social data for EU members at both the national and sub-national/regional level. Some of its databases also include data for countries in Central and Eastern Europe. Much of their data are accessible on-line here. The EDC also has a DVD database with more extensive time-series coverage. The DVD database has an on-line interface. Please note that none of the interfaces is entirely user-friendly.
OECD (Organization for Economic Cooperation and Development) Fiscal Decentralisation Database
"The OECD fiscal decentralisation database provides comparative information on the following indicators analysed by level of government sector, [Federal or Central (including Social Security), State/regions and Local] for OECD member countries between 1965 and 2011." The data are national-level data that provide estimates of total government spending various levels - central, state/region, and local.
OECD (Organization for Economic Cooperation and Development) iLibrary
The OECD iLibrary is an online interface that provides full-text access to OECD studies, periodicals, and dozens of statistical databases via OECD.Stat. The topical range of the iLibrary is considerable and covers areas such as agricultural policies, environmental indicators, social expenditures, labour markets, national accounts, foreign trade and FDI, and various industry-level data. The various OECD.Stat databases include collections for regional data and measures of fiscal decentralization.
Party Government Data Set (PGDS)
The Party Government Data Set, hosted by J.J Woldendorp at the University of Amsterdam, "covers 39 parliamentary democracies from 1945, or the year these countries became a parliamentary democracy (again), through 2008." The geographic focus is on countries in Western and Eastern Europe. The data cover topics such as reason for government termination, ideological orientation of government, names of parties in government, and size of governing coaliation (e.g. minority governments).
Quality of Government (QOG) Institute
The QOG Institute is hosted by members of the Department of Political Science at Göteborg University in Sweden and is devoted to "the causes, consequences and nature of 'good governance.'" The Institute has created four collections of data on governance: a broad collection of governance indicators that is global in coverage; a more narrow collection that focuses on social policy in wealthier countries; data from expert surveys on politicization and professionalization of public administration in individual countries, and a new data collection on perceptions of corruption in individual regions within EU members. The data are compiled from multiple sources, including the Polity IV Project, the Cingarelli-Richards Human Rights Data, Transparency International, Freedom House, various international organizations, and datasets produced by various academics. The QoG data are available in SPSS, Stata, and comma-delimited (.csv) formats. The Institute has also compiled a very nice collection of links to other governance-themed data (some free, some fee-based) compiled by various sources.
Regional Authority Index (RAI)
The Regional Authority Index "measures the formal authority of intermediate or regional general-purpose government [and] tracks regional authority on an annual basis from 1950 to 2010 ... [it] is a measure of the authority of regional governments on an annual basis across eight dimensions: institutional depth, policy scope, fiscal autonomy, representation, law making, executive control, fiscal control, constitutional reform." Data are coded at both the national and regional levels. The data are also available via UNC-Chapel Hill.
Centro de Investigaciones Sociológicas (CIS)
The CIS is a quantitative data archive located in Madrid which houses data from surveys on topics such as elections, health, crime, and monthly "barometers" of public opinion. Be advised that access to data files may be conditional upon payment of fees. Some CIS data are also available via the Roper Center for Public Opinion Research.
European Social Survey (ESS)
The ESS is a recurring survey series conducted within countries in Western Europe, as well as in post-communist countries in Central/Eastern Europe, the Baltics, and in Turkey. To quote the website, the ESS is "designed to chart and explain the interaction between Europe's changing institutions and the attitudes, beliefs and behaviour patterns of its diverse populations." The survey includes standard demographic questions (e.g. age, ethnicity) and sub-national regional identifiers, and covers topics like immigration, vote choice and party affiliation, political participation and civic engagement, "values," and feelings of identity/exclusion. The data are available for free upon registration at http://ess.nsd.uib.no/. There is also an ICPSR study that took data from a survey on civic participzation in the U.S. and matched it with data from the 2002 European Social Survey for those questions which were common across them.
ICPSR (Inter-University Consortium for Political and Social Research
The ICPSR at the University of Michigan is one of the largest archives of quanitative data in the world, with an eclectic range of holdings that covers topics such as health care, demographics, crime, public opinion, and even the size of horses in the Habsburg Empire.
Leibniz Institute for the Social Sciences (GESIS)
GESIS is one the premier data archives in Western Europe. It is the principal repository for collections such as the Eurobaromter series of polls in European Union members. It also has a variety of historic data sources, such as a large collection of data from the German Democratic Republic and a similar collection of studies for pre-WWII Germany. GESIS is also a member of the Council of European Social Sciences Data Archives.
Mannheim Eurobarometer Trend File, 1970-2002
The Eurobarometer is an ongoing series of polls of public opinion in European Union member states, and is usually conducted twice a year. Eurobarometers generally mix questions about European/EU integration and EU institutions with questions about specific social/political/economic issues. The Mannheim Trend File is a compilation of data and questions from Eurobarometers conducted between 1970 and 2002, with an emphasis on recurring questions from those surveys about attitudes towards the European Union. Data and documentation for this collection are available via the ICPSR, and also via the Electronic Data Center. Data files are available from the German Social Science Infrastructure Services (GESIS). GESIS also has a search engine for Eurobarometer codebooks and questionnaires that is very useful for identifying the topical contents of individual studies.
UK Data Archive (UKDA)
The UK Data Archive is another of the premier data archives in Western Europe, with a wide-ranging and eclectic collection covering topics such as the finances and trade of the East India Company, the fiscal straits of European governments in the Middle Ages, Orange Order membership in Northern Ireland, and interviews with black immigrants to Britain in the 1800's and 1900's. The UKDA is also a member of the Council of European Social Sciences Data Archives.
World Values Surveys Series
The World Values Survey is "a worldwide investigation of sociocultural and political change. It is conducted by a network of social scientist at leading universities all around world. The survey is performed on nationally representative samples in almost 80 societies on all six inhabited continents." It is an excellent source for cross-national survey data and is a widely-referenced resource. Some WVS waves also include samples for specific regions within individual countries. Data from the WVS are available for free upon registration. Documentation for the data are available here and here. The Data Center also has data from all four "waves" of the World Values Survey available here.