[IronJack]

"The Last Full Measure" by Jeffrey Shaara
Bruce Catton's Trilogy, "The Coming Fury", "Terrible Swift Sword", and "Never Call Retreat." "Silence at Appomatox" is superb as well.
Somebody already mentioned Shelby Foote's trilogy, which frankly I found dry and tedious, strangely at odds with Foote's charming personality.

That will keep you busy for a while. I have several encylopedias of the Civil War too, excellent for quick reference or a good overview.

[Reily]

Catton also did a wonderful biographical series on Grant!

[StoneWall Brigade]

I`m currently enjoying the trilogy of civil war books written by LT. Col Ralph Peters