Great read - some contemporary South Africaans use "Apple computers" to go back to 1861 and equip Rebels with AKs.
Yes, Guns of the South is a great book.
A better one, also by Turtledove, is “How Few Remain”, which sets up a scenariom where Lee wins at Antietam/Sharpsburg because his orders aren’t intercepted. Resulting in Southern independence but also a second war in the 1870s when the CSA annexes Norther Mexico to provide a path to the Pacific.
The follow-on books to that (North and South fighting on opposite sides of WWI and II) arent as good, but still a decent enough hypothetical extrapolation.
On a more historical bent and without science fiction I recommend as “alternate histories:”
Newt Gingrich & William Fortschen’s civil war trilogy see:
http://en.wikipedia.org/wiki/Gettysburg:_A_Novel_of_the_Civil_War
Or Peter Tsouas’ civil war trilogy: the 3rd volume of which was just published.
http://www.amazon.com/Britannias-Fist-Civil-Alternate-History/dp/1574888234
Read Turtledove’s “Southern Victory” series starting with “How Few Remain”. It’s a great alternate history series, which continues on I other series to explore the results of a Confederate victory all through the Civil, Spanish American, and Great war, among others.