Check out these great resources for Social Studies:
State Historical Society of Iowa: This website has Primary Source Sets already created and aligned with the Iowa Core Standards and is a great resource for Iowa History
Library of Congress: This website has an impressive collection of primary sources with collections on just about any topic.
National Geographic: This website has a variety of resources and collections for all grade levels in a variety of categories.
PBS Learning Media: This website has resources on a variety of topics including Civics/Government, US History, World History, Elementary Social Studies, Geography, and Economics.
Blue Feed, Red Feed: See Liberal and Conservative sides of several social issues, side by side.
New Social Studies Resources...
History Dilemmas: A collection of historical dilemmas that ask students to make tough decisions.
Thinkalong: Using trusted source materials from PBS, NPR and local public media stations, Thinkalong is a free program that helps students think critically about media, develop informed opinions, and practice respectful, civil discourse.
AllSides: Provides unbiased, balanced news from all sides: from the left, from the right, and from the center.
Primary Source: This website has resource guides on a variety of topics focusing on global citizenship.