Digital Social Studies Content

As more and more of our world and classrooms go digital and more and more devices make their way into the classrooms I'm always looking for apps and sites that deliver that content...usually the free ones.  Today while reading FreeTech4Teachers.com I read about GoSocialStudiesGo.com, which is a free site that has a lot of good Social Studies content.  Their site says they have over 100 topics, with videos, primary sources, games and links.  I spent some time wandering around their site and it's pretty good.