The Internet Text Archive has some Indiana regimental histories in their database. Just enter Indiana Civil War in the search box and then search. I found histories for the following regiments: 3rd Cavalry, 7th Cavalry, 6th Infantry, 12th Infantry, 31st Infantry, 37th Infantry, 46th Infantry, 51st Infantry, 70th Infantry, 82nd Infantry, 99th Infantry, and 100th Infantry along with several volumes of the Indiana Adjutant General's reports. The books can be read online or downloaded in various formats.