1. The Army of the Potomac: Order of Battle, 1861-1865, with Commanders, Strengths, Losses and More by Darrell L. Collins (McFarland, 2013).
Collins has compiled an AoP OB for all its major campaigns in a single oversize volume, using the O.R., Dyer's Compendium, and Heitman's Historical Dictionary and Register of the United States Army. If you're offended by McF's paperback pricing model, don't look at this one!
2. "In Her Hour of Sore Distress and Peril": The Civil War Diaries of John P. Reynolds, Eighth Massachusetts Volunteer Infantry by John P. Reynolds, edited by Jeffrey L. Patrick (McFarland, 2013).
This is a rare regimental history of an 1861 90-Day regiment, expressed through the diaries of a soldier serving under Benjamin Butler. Patrick contributes voluminous explanatory notes to what is a welcome first hand account of the important Union operation that secured eastern Maryland and its lines of communication to Washington.
3. The Black Experience in the Civil War South by Stephen V. Ash (Potomac, 2013).
"Drawing on memoirs, autobiographies, and other original source materials, Stephen V. Ash details the experiences of blacks who took up residence in Union “contraband camps” and on free-labor plantations and those who enlisted in the Union army."
4. A Civil War Round Table Quiz Book by Dave Smith (Potomac, 2013).
"The book features 117 different quizzes, the subjects ranging from the infamous Dred Scott case to the final surrender at Appomattox Court House. Each quiz has a theme, and the themes have been selected to cover myriad subjects and to lead readers into the lesser-known aspects of the war that they might not otherwise explore."