Christ in the Old Testament: Old Testament Appearances of Christ in Human Form by James A Borland and published by Christian Focus Publications.
This is a book that focuses on God's appearances in human form rather than the shekinah, the pillar of cloud or other manifestations of God's presence. Its purpose is to present a positive theology of theophanies rather than simply a defence against erroneous views. Borland looks at the characteristics of Christophanies and their use by God. It is the most comprehensive book of its type, although not every Christophany is investigated all categories are represented.