I stopped at Gettysburg, PA, in October 2009 on a trip back East to visit family. I grew up close to Gettysburg and always liked visiting the battlefield reading about what happened there, and then walking the battlefield - it was always such a moving experience.
For people that don't know, Gettysburg was the pivotal battle in the American Civil War. It took place, by accident, in July 1863 in a small crossroads in south central PA. It lasted three days and resulted in an incredible number of casualties on both sides. Like many other places I visited, if you have a chance check it out - it is worth it!