The Council of European Social Science Data Archives Catalogue
http://www.cessda.org/accessing/catalogue/

UK data archive
http://www.data-archive.ac.uk/about/about.asp

Inter-University Consortium for Political and Social Research (ICPSR)
http://webapp.icpsr.umich.edu/ICPSR/

German Social Science Infrastructure Services Association (GESIS)
http://www.gesis.org/en/institute/

Norwegian Social Science Data Services (NSD)
http://www.nsd.uib.no/nsd/english/index.html