World History for Us All - Primarily provides resources for teaching the middle school and high school curriculum.
National Council for Social Studies - Lesson plans arranged by historical period and grade band as well as other resources.
Mission US - offers two interactive journeys through two important eras in U.S. History. The journeys are designed as role-playing games or missions. The first mission in Mission U.S. is set in Boston in 1770. Students play the role of 14 year old Nat Wheeler who, after the Boston Massacre, must choose to side with the Loyalists or the Patriots. The second mission in Mission U.S. is set in Kentucky and Ohio in 1850. Students take on the role of a fourteen year old slave named Lucy. In the mission students escape slavery in Kentucky and navigate to Ohio.
European Exploration in the Age of Discovery - A free iPad app that puts students in charge of exploring the "New World." In the game students are in charge of selecting explorers and ships to send out to the New World. Students have to manage the finances of their expeditions so that they don't run out of money before they can return home safely. European Exploration: The Age of Discovery provides students with historical information about the explorers that are available to lead expeditions. Some of the explorers available include Giovanni da Verrazano, Christopher Columbus, and Juan Ponce de Leon. The explorers are graded based on their navigation, cartography, and shipkeeping skills. Each explorer has a different salary which students must account for when managing the budgets of their expeditions. The object of the game is to unveil the entire New World. To do this students draw expedition maps and send out their explorers. If the expedition is successful it will earn money that students can then parlay into financing another expedition. Successful managers of European Exploration: The Age of Discovery will be able to manage multiple expeditions simultaneously.
The History Place. A variety of resources (including timelines of significant events) for mainly U.S. History, but also World History.
U.S. History.org. This website provides timelines with hyperlinks to explore that event further. It also provides lesson plan resources for teachers. Primarily a resource for the American Revolution. Something cool about this site is that it provides a visual of the rough draft of the Declaration of Independence (a great resource for showing students that even our founding fathers edited their drafts!)
The American Revolution.org. Thorough website that provides a wide variety of resources for teaching the American Revolution.
Stanford University History Lessons. This resource has lesson plans on a wide variety of U.S. History ranging from Colonial times to the Cold War as well as World History from Egyptian to Roman.