Team of Rivals
One of the most highly regarded books amongst Gordon Brown's supporters is Robert Caro's biography of Lyndon Johnson. The three volumes that have been published so far have been beautifully written and range far beyond Johnson's life to the story of depression-era America, Texas in the early fifties, his early political campaigns, and the workings of the American Senate amongst much else.
Unfortunately, in thirty-odd years and three volumes, Caro has only managed to get to 1959 in Johnson's life, so the Brownites haven't got to read about how Johnson became President (probably a good thing for Tony Blair, that) and his successes and failures as President.
Since it doesn't look like the remaining volumes will be written in time before the leadership contest is settled, may I humbly recommend 'Team of Rivals' by Doris Kearns Goodwin to Brown and any other contenders for the leadership. It is the story of how Abraham Lincoln managed to best his more highly regarded rivals to secure the nomination for the Presidency, and then how he managed to persuade each of them to serve in his cabinet and devote their considerable abilities to the service of their country at a time of unprecedented challenges. It's an excellent story, told well, and a welcome antidote to the events of the past few weeks in the Labour Party.