Richard Rhodes (Simon & Schuster, 1986)
This is the definitive work on the subject. Yes, it's long (over 800 pages) and not an easy read, but Rhodes writes in a gripping style and delivers facinating psychological insights into the personalities of the men behind the Manhattan Project. Rhodes covers it all: the theoretical origins of the bomb in the mind of Leo Szilard, the lab experiments spearheaded by Enrico Fermi and his crew of scientists at the University of Chicago, the building of the prototype, the test at Alamagordo, New Mexico, the training of the B-29 crews assigned to deliver the first two bombs and the missions themselves. He also delves into the struggle in Nazi Germany and Imperial Japan to make the first bomb, as well as the political and military events that led to the destruction of the Japanese cities of Hiroshima and Nagasaki. Well worth the time and effort.
Brian VanDeMark (Little, Brown, 2003)
VanDeMark puts his focus on the nine men who built the atomic bomb and how each struggled with the implications of their deadly creation. He does an excellent job of bringing these brilliant scientists to life in this examination of the moral ambiguity that exists in "an imperfect world that sometimes forges good from evil and evil from good." First, we witness science at work, in the act of creation that drove these talented individuals. However, then VanDeMark switches gears and tackles the issues of the aftermath, when the scientists, academics all, realized the real-world horrors and implications for the future that their creation had wrought. Pandora indeed.
Stephen Walker (Harper Collins, 2005)
This high-speed rollercoaster ride of a narrative recreates a (literally) minute-by-minute retelling of the Hiroshima bombing as remembered by American soldiers, Los Alamos scientists, and Japanese survivors. He examines the doubts and fears of the bomb's designers, the thought processes behind the selection of the targets, and the bewilderment of citizens of Hiroshima, who were victims not only of the U.S. bomb, but a Japanese government controlled by men who were determined to continue the fight at all costs.