Here are some of the more relevant and important political science websites. Please let me know if any links are broken, and please feel free to offer suggestions for additional sites.
American Political Science Association (APSA)
Consortium of Social Science Organizations (COSSA)
Foreign Policy Research Institute (FPRI)
Institute for the Study of Conflict, Ideology, and Policy (ISCIP)
International Peace Research Institute, Oslo (PRIO)
International Political Science Association (IPSA)
International Studies Association (ISA)
Midwest Political Science Association (MPSA)
National Council for the Social Studies (NCSS)
Oklahoma Political Science Association (OPSA)
Society for the Study of Social Problems (SSSP)
Southern Political Science Association (SPSA)
Southwestern Political Science Association (SWPSA)