The World Association for Public Opinion Research is an international organization that promotes the freedom to conduct and publish public opinion research in every country of the world. WAPOR publishes the International Journal of Public Opinion Research and holds annual conferences and regional seminars.
The Roper Center for Public Opinion Research is an archive of data from surveys of public opinion since the 1930's. Much of the content requires a subscription, but the site still includes some free content:
The National Council on Public Polls is an association of polling organizations. Its members include Gallup, Roper, Pew and most major media outlets. Part of NCPP's mission is to increase understanding of how polls are conducted and interpreted.