British

• data.gov.uk has official government datasets
• ESRC Society Today, combines information from the ESRC Awards and Outputs Database (formerly Regard) the "old" ESRC website, and a variety of other data sources and sites
• European Consortium for Political Research
  • List of ECPR Standing groups
  • ECPR Senior Academic Network in Europe (SANE)
  • ESRC Data Archive
• Essex Summer School in Social Science Data Analysis and Collection programme
• British Election Studies, 1963-1992
• British Election Survey
• UK PSA's Elections, Public Opinion and Parties (EPOP)
• Centre for Applied Social Surveys
• Centre for Research into Elections and Social Trends (CREST)
• A Guide to Longitudinal Resources
• The National Centre for Social Research
• Qualidata - Qualitative Data Service, ESRC qualitative data archival resource centre.
• Straight Statistics
• MIMAS On-line access to many large and complex data sets.
• UK Home Office - Research and Statistics Department
• Department for work and Pensions Statistics
• National Statistics Online

European

• BDSP
• Danish Data Archives
• EULib, a private, non-commercial project aimed at automatically collecting and categorizing information about the European Union
• EURODATA Research Archive, Mannheim Centre for European Social Research
• Eurobarometer continuous tracking of European opinion
• Dutch opinion polls (in Dutch)
• NSD (Norwegian Social Science Data Services). Not all information is available in English
• Swedish Social Science Data Service

Other Archives

• American National Election Studies
• Canadian Opinion Research Archive
• Center on Policy Attitudes
• Constituency-Level Elections (CLE) Dataset, Washington U, St Louis
• COW: Correlates of War datasets
• Country Indicators for Foreign Policy
• DataCards is a structured collection tool that indexes data sources that relate to irregular warfare, assessment, or can be used for socio-cultural modeling. It is a username and password protected site, but anyone can request (and will be granted) said username and password
• Gapminder: a fact based world view
• ICPSR
• ICPSR General Social Survey Codebook
• Harvard-MIT Data Center
• National Election Studies. US data on voting, public opinion, and participation
• NORC, a national organization for research at the University of Chicago
• Odum Institute Data Services
• Public Policy Mood Time Series Data, James A. Stimson
• Statistical Resources on the Web. Includes politics, demographics, economics, education
• The Record of American Democracy, 1984-1990 (ROAD) aggregate data set on American politics
• Research Resources for the Social Sciences.
• Search Free Public Records
• Socioeconomic Data and Applications Center (SEDAC)
  • Understanding the World Today has links to free data, and also its own data sets
  • World bank Social Indicators of Development
• Social Science Data Analysis Network
• Social Sciences Data Collection, UC San Diego. On-line opinion polls, election surveys, etc., from the US, Britain, Canada, Germany, Netherlands.
• Statistical Resources on the Web
• StatLib index
• UC Data. UC Berkeley's principal archive of computerized social science and health statistics
• USNSI data archive
• US Unemployment rates, Google's Public Data search function
• World Bank Social Indicators of Development and Trends in Developing Economies Database of Political Institutions
• WWW V-L Statistics page

Polling Organisations etc

• 20 Questions A Journalist Should Ask About Poll Results, or indeed anyone
• American Association for Public Opinion Research
• Center for Survey Research, Indiana
• CIS·Centro de Investigaciones Sociológicas, Barometer Indicators
• CMOR, Promoting & Advocating Survey Research
• Eagleton Center for Public Interest Polling
• ComRes Poll Digest
• Gallup publish survey results on the Internet and take Internet surveys
• Guides to published public opinion and other data
• HarrisInteractive
• ICM
• Latin American Public Opinion Project, Vanderbilt University
• MORI
• GfK NOP
• National Network of State Polls
• Odum Institute Public Opinion Poll Question Database
• Peil.nl, Netherlands
• Politieke Barometer, Netherlands
• Public Opinion Polling in Canada, a review by the Parliamentary Research Branch
• Public Opinion Pros, an online magazine for the polling professional (and everybody else). Now defunct: this is an archive
• Roper Center for Public Opinion Research
• SenseUS. Emotional Response Polling measures the emotional connection between potential voters and presidential candidates
• USA Election Polls
• What is a Survey, booklet based on material by the ASA
• World Association for Public Opinion Research
• Zogby International, opinion research

Population Studies

• The current world population is estimated to be approximately 6,992,156,811
• Population Studies Centre, University of Michigan
• The Population Index
• US Bureau of Census and the Census FactFinder, and 2000 gateway. Also World POPclock and maps
• US CensusCD 2000
• LocalCensus.com, has statistical information for a wide variety of categories pertaining to the USA
• DataFerrett
• World population density
• 1901 Census, England and Wales

Software

• CAQDAS - Computer Assisted Qualitative Data Analysis Software.
• CLUSTAN Cluster Analysis software
• The Democracy Game, strategy software and forum
• Econometric Software Links, from the Econometrics Journal
• gSwing, a Java program for viewing elections results and a collection of tools for maintaining the election data. gSwing is free, open source and platform independent
• instantAtlas, offers graphical presentation of a range of electoral and political statistics
• Minitab
• SAS
• SDA: Survey Documentation and Analysis
• SPSS
• Statistical Software
• Statsoft: Statistica - high performance statistical software
• UKElect election analysis and forecasting software
• Mark Miller's VBPro programs for content analysis.

Miscellaneous

• American Statistical Association
• Analyzing U.S. 2008 Elections with Mathematica
• Classification Society of North America. Promotes the scientific study of classification and clustering
• Data Mining in Politics
• Digital Vector Maps, the site sells editable royalty free maps, including Congressional District maps, world maps, etc.
• FiveThirtyEight.com, Electoral Projections Done Right
• International Association for Social Science Information Service & Technology
• Kovak Computing Services: their page includes links to a number of statistical sites, including sources of shareware and public domain statistics software, as well as giving information on their own products
• The PCL Map Collection has over 230,000 maps covering every area of the world
• Social Research Update is a quarterly electronic journal that covers new developments in social research
• Understanding Correlation, RJ Rummel
• Understanding Factor Analysis, RJ Rummel
• US National Trade Data Bank
• Washington Post Data Directory