The most popular artefact from my archaeology talk the other day was this American Civil War lead bullet. My friend Shelly's husband found it along the Appalachian Trail in Harper's Ferry. It's in perfect condition, although it has a white oxidised (or whatever lead does) layer on the surface. All the history of the Civil War, and of Harper's Ferry, aside, the thing that most strikes people is how heavy it is. Certainly the kids had no idea about its context, but they loved how it feels in the palm of your hand. The bullet also reminds me of Harper's Ferry, which I enjoyed visiting enormously, and of course Shelly - so its story continues even though it has fulfilled its original function!
A little online research just now suggests it's a .54 caliber 3-ring Minie (or Minié) ball, very common, used by both sides.