Adams County (Pennsylvania): See
The Plain and Fancy Farm provides a good all-around tour of the Amish community including a restaurant, bus tours and a movie. Particularly good if you're a foreign visitor without a car.
The Gettysburg National Military Park, just south of Gettysburg, is one of the most famous battlefields of the American Civil War. The National Apple Museum, north of Gettysburg, has exhibits on the apple industry in the region, and a recreated 1880s farm kitchen and a General Store.