For theology, I'd recommend:
Vladimir Lossky's The Mystical Theology of the Eastern Church.
John Meyendorff's Byzantine Theology: Historical Trends and Doctrinal Themes.
Alexander Schmemann's For the Life of the World: Sacraments and Orthodoxy.
For history, I'd recommend The Church in History series edited by John Meyendorff, particularly:
vol 2, John Meyendorff, Imperial Unity and Christian Divisions: The Church AD 450-680
vol 3, Andrew Louth, Greek East and Latin West: The Church AD 681-1071
vol 4, Aristeides Papadakis, The Christian East and the Rise of the Papacy: The Church AD 1071-1453