The Kennedy Farm - about 4 miles north of Harper's Ferry, where John Brown and his men hid out before the raid in 1858. I believe it's privately owned - google for "Kennedy Farm" and "John Brown" for the details.
Antietam - Burnside's Bridge area, go across to the heights west of the creek and look down.
Somewhere in that vicinity is a huge monument to Sergeant Willliam McKinley, who apparently served coffee while under fire. It's nice to be the president.
My family owns some land near Pickens, West Virginia, but it's been 40 years since I was in that vicinity....