Website highlights Social Studies (Geography, United States History, World History, Economics, and Government) sites. In order to make the list, these sites have to be accessible and challenging to English Language Learners and native-speakers alike.
This site has a lot of different games students can play to quiz themselves. Once you choose the subject, you then pick which type of game you want to play. There are geography games, trivia games and much more.
This is a helpful cite for world history teachers specifically. It has some sample lessons as well as some additional resources for how to teach a world history class and help make it interesting.
This is a website that describes geocaching, which is a real life communal treasure hunt around the world. It involves the use of gps to find these "geocaches" in predestined areas. This can be an excellent tool in your class incorporated with your content in any core subject.