Killer Angels by Michael Shaara

Probably the best fictional book on Gettysburg ever written, the inspiration for the Turner mini-series Gettysburg with Martin Sheen and Jeff Daniels. After his death, his son Jeff wrote two prequals, Gone for Soldiers and Gods and Generals, and a sequal Last Full Measure.

The generals you read about in school, Lee, Chamberlain, Longstreet, Picket, etc. are all alive in this book. You see the battle through their eyes, what they were doing and thinking during the most important battle of the Civil War. The relationships of the generals on the same side as well as their old friends now on the other side are explored.

The Sharras' Civil War books are special to me because the original Bob Andrepont (Cleophas Andrepont, but they called him Bob) was in the 2nd Louisiana and fought in many of the battles they write about. Also my favorite Union general, Joshua Lawrence Chamberlain is featured in them.