Battle Cry of Freedom: I am fairly well-read on the ACW, but I learned LOTS from this one. My highest recommendation.
Shelby Foote's trilogy: I have NEVER been as engaged when reading history, and I read a LOT of history. My highest recommendation.
Landscape Turned Red: An outstanding account of the day's events, as well as terrific insights into the before and after of the battle. I used it as my guide book for my own personal 'staff ride' on Antitam National Battlefield. My highest recommendation.
Team of Rivals: Reading it now. The most important aspect of the ACW, the political angle in Washington. More than any other battlefiled, HERE is where the war was guided and decided. If you want to understand the War, don't read about the famous battles; read about the politics. My highest recommendation.
The Killer Angels: Right behind my Flashman, Hornblower and Aubrey series, there's THIS incredibly vivid and engaging account of the personalities and the realities of the Gettysburg Campaign. I never thought a work of fiction could teach me this much about my most beloved are of study, but Scharra is faithful to and is singulalry eqipped to tell the story. My highest recommendation.
Gingrich's Gettysburg: Worth reading for the alternate historical outcome. I enjoyed it, and it certainly is a tale that captures all the 'waht-ifs' that the battle has generated ever since Pickett marched into glorious destruction. Recommended.
If y'all think I was too free with the 'My highest recommendation', think again. shek has managed to list the absolute top-flight list of the books I have personal knowledge of, and it is no exageration to say that at the completion of each of the ones I've listed, you'll know what all Americans SHOULD know about the most crucial aspect of their history, and WHY it has made us into the country we are today.
Well, actually...you may want to read those first two through TWICE. I did, and came away with even more than the first time.