Not exactly a reenacting subject, but something that should impact our hobby profoundly is military archaeology. This blog has touched on it a couple times with Isaac Mason and Elena Filitova's great site on WW2 Eastern Front photos. With my article on forensic reenacting, this should be a field that reenactors need to keep an eye on very closely.
There are an abundance of good Russian and Ukrainian sites devoted to excavating WW2 remains. Military Archaeology is a good site to check out what the amatuers are doing, and how they're doing it. Personally I don't recommend this kind of digging, I'd prefer to have a university come in and do it, but it is still interesting. The Russians dig up some great things, though.
The National Museum of Military History in Luxembourg has a great site that covers WW2 Western front efforts. There is also a great online forum devoted to military archaeology.
On the American Civil War side of things, the Center for Heritage Resource Studies has a great site on excavating some Civil War sites and updates on those efforts. The CSS Neuse is another site to keep tabs on, it's still an on-going project.
As reenactors, it behooves us to keep up with the latest and greatest finds. Such finds may not be as dramatic as items from the ancient and medieval periods, but they do represent new pieces of information we need to consider for our personal and prop impressions.