The Tennessee State Library and Archives has launched an awesome new project:
The first of its kind in the nation, the Tennessee Civil War Geographic Information System (GIS) Survey shows hundreds of locations where Civil War battles, engagements, skirmishes and other military actions took place. The interactive GIS application for the Civil War in Tennessee is now available at: http://tnmap.tn.gov/civilwar/.
The web site allows modern aerial photography, street maps and land use maps to be overlaid onto sites where Civil War actions occurred in Tennessee. It also links narrative information about these events from the Tennessee Civil War Sourcebook. Complete accounts of all the state units that served in the war are searchable by county along with 1860 United States Census data.
This is one of the most comprehensive and useful online historical tools I’ve ever seen. You can select any engagement and get its location on a modern-day aerial, street, or terrain map, along with primary source material; instantly access unit histories relevant to each county; see the locations of historic markers across the state; and more.
I clicked on my home county and found OR reports for actions in my hometown, along with descriptions of all the units that included local boys. Pretty cool! Go check it out.
Past in the Present 
I had a chance to give this a test run back in May:
http://posterityproject.blogspot.com/2011/05/tennessees-civil-war-gis-app-is-up-and.html
I agree with you, it is an incredible online tool for research, just one of the many reasons TSLA is among the best archival resources available.
This is wonderful and I wonder if the State will ever do something like this for the skirmishes or historical markers of the 18th century.
I certainly hope so. I’d love to be able to track down all those Indian battles and raids from the Revolutionary period. An online map with all the forts and stations would be tremendously helpful.
–ML