Two good books from among many to stimulate discussion and prayer about the priesthood:
Pope Emeritus Benedict XVI homilies about priesthood over the sixty years of his own priesthood, Teaching And Learning The Love Of God, highlight the important spiritual aspects of priesthood. Though the priests about whom the pope preached will likely be unknown to us, the message about priesthood is a universal one and gives insight into the thinking of the pope.
Written by a diocesan priest who served in a parish, then as Vocation Director and at the time of writing Vice Rector of a Catholic major seminary, To Save A Thousand Souls is a very practical look at the questions, fears and thoughts a man has who is discerning whether God might be calling him to diocesan priesthood.
The anecdotes describing what a priest does are particularly helpful in stimulating prayer and discussion about priesthood and the book gives insight into the process of application and training of a priest even if these particular steps might be a bit ahead of the man's discernment.