I highly recommend both "Storm of Steel" (best first-person view of the war) and "Dreadnought" (best telling of the majestic story of the runup to the war).
Just finished The Sleepwalkers about the diplomatic and political maneuvers from about 1900 on. I would strongly recommend Paul Fussell's The Great War and Modern Memory for reflections on the writing that came out of and around the war.
