These resources are particularly appropiate for elementary social studies instruction.
History
America's Story from Americas Library
Government and Law
Ben's Guide to the U.S. Government for Kids
U.S. House of Representatives: Educational Resources
National Crime Prevention Council
Geography
Blank Maps of Countries and States
Economics
Escape from Knab (Investing and Saving Decisions)
Economics and Geography Lesson for 32 Children's Books
Anthropology, Sociology, and Psychology
Peace Corps Global Education World Wise Schools
Dig: The Archaeology Magazine for Kids
American Psychological Association - for Kids
The following resources provide background information and suggested teaching methods on a number of controversial topics.
Controversial Issues - Multnomah Public Library
Fighting Hate Across the Nation
Teachers Tool Kit Emphasis
We Hold These Truths to Be Self-Evident
Current Events in the Social Studies Classroom
PBS TeacherSource: Social Studies
Experiencing the Legal System: Fairy Tale Trials for 5th Graders