Using the self-publishing service CreateSpace, various U.S. military institutions like the U.S. Army Command and General Staff College, Naval War College and others have embarked on something of a printing spree of late.
A few examples of what's been made available:
* First Kansas Colored Volunteers: Contributions of Black Union Soldiers in the Trans-Mississippi West
* The Use of the Virginia Military Institute Corps of Cadets as a Military Unit Before and During the War Between the States
* The Confederate King of Battle: A Comparison on the Field Artillery Corps of The Army of Northern Virginia and the Army of Tennessee
* Shared Blame (Inertial Leadership, Indiscipline, and Horse Blinders): The Failure of the "Other" Confederate Cavalry Brigades During the Gettysburg Campaign (28 May-1 July 1863)
* Naval Strategy During the American Civil War
* The Tullahoma Campaign: The Beginning of the End for the Confederacy
Some, like those from the CGSC, used to be available as free downloads and maybe still are. One that caught my attention in particular is Jeffery Price's MA thesis A Courage and Desperation Rarely Equaled: The 36th Arkansas Infantry Regiment (Confederate States Army). As far as I know, no regimental history of that unit has been published before.