We've mentioned it before, but it bears repeating that the U.S. Army Center of Military History's website contains some first rate reading and research materials. Most of what you need can be found off of this page.
You want to read the best study on black troops in World War II? Here it is. How about the Women's Army Corps? Right here. The Army's history of Guadalcanal, Okinawa, the Battle of the Bulge, the Middle East Theater, and many others are all available, searchable, and unabridged. All of CMH's histories of the Korean War are online. If you prefer a history of institutional development, this page includes, among other things, a link to From Root to McNamara: Army Organization and Administration.
Unfortunately, many of these books are not well known because they are not advertised by the government. Additionally, too many people dismiss them because they are official history. Take a look for yourself--you will find thoughtful, critical, well-researched studies. This is an excellent resource, and I'm not just saying that because I worked for CMH (none of the stuff I did is on the website, but I will let you know if that changes).