I've been a student of Abraham Lincoln since I was four years old. Here are my four favorite Lincoln books:
1. Lincoln: David Herbert Donald's 1996 biography is the magnum opus of a scholar who has spent a lifetime studying the sixteenth president. Donald's thorough research is matched with his informed and analytical mind and his gifts as a writer. Novices and afficiandos alike will derive much from reading this work of a great historian.
2. With Malice Toward None: A Life of Abraham Lincoln. This is another worthy one-volume telling of Lincoln's life. First published in the late-70s, it was written by Stephen B. Oates.
3. Lincoln at Gettysburg: The Words That Remade America. I've discussed Garry Wills' phenomenal examination of one of Lincoln's most important speeches--and arguably the nation's most important speech--here.
4. The Day Lincoln Was Shot by Jim Bishop. This journalist-eye's view of the twenty-four hour period when the sixteenth President was assassinated is a great read. Here, you learn something of the conspiracy, the manner in which the President haplessly slipped into the cross-hares of his assassin, and share in the sense of loss and anger that engulfed much of the United States when Lincoln became the first American president to be murdered.