The U.S. Library of Congress offers a wealth of fantastic online resources for teachers and students. A quick jump into the teachers resource page will lead you to things like these primary source analysis guides that I have used with students in the past. The LOC also offers a couple of good iOS apps that are worth noting.
Library of Congress–Virtual Tour provides images of the Library’s historic rooms along with historical information about them. The images are also paired with related links for further investigation. Audio podcasts about items and features in each room can be accessed through the LOC Virtual Tour app.
Aesop’s Fables interactive book from the Library of Congress is available to read on the Web, on an iPad, and on an Android device. The book contains more than 140 of Aesop’s Fables for children. The level of interactivity varies widely depending upon which story you’re reading. Some of the stories have truly interactive animations while other simply have a small moving picture accompanying the fable.