I'm very impressed with Timothy Laniak, Shepherds After My Own Heart: Pastoral Traditions and Leadership in the Bible (IVP, 2006). It's a great survey of the shepherd metaphor in the ANE world, in Israel under Moses and the Davidic kings, in the hope of restoration of the postexilic prophets, in the person of Jesus, and in his servants who live and die in the service of his people as did “the slain Lamb and ruling Shepherd.”