Longobard Pagan Resistance:
- Stefano Gasparri La Cultura Tradizionale dei Longobardi: Struttura Tribale e Resistenze Pagane ("Traditional Longobard Culture: Tribal Structure and Pagan Resistance") (1989)
- Stefano Gasparri I duchi longobardi (1978)
- Stefano Palmieri Duchi, principi e vescovi nella Longobardia meridionale ("Dukes, princes and bishops in southern Longobardia"), a Chapter in Longobardia e longobardi nell'Italia meridionale: le istituzioni ecclesiastiche (Vita e Pensiero, 1996)
- Jörg Jarnut, Storia dei Longobardi (2002)
- Pohl, Walter. "Deliberate ambiguity: the Lombards and Christianity." In Christianizing Peoples and Converting Individuals, ed. Guyda Armstrong, pp. 47-58. Turnhout: Brepols, 2000 (overview and full table of contents of that book is at byzantineee.blogspot.com)
- Pohl, Walter, "Memory, Identity, and Power in Lombard Italy", in The Uses of the Past in the Early Middle Ages, ed. Yitzhak Hen, Matthew Innes
- Stefano Gasparri, Kingship rituals and ideology in Lombard Italy, in Rituals of power: from late antiquity to the early Middle Ages, ed. Frans Theuws, Janet L. Nelson (Brill, 2000)
- Walter Pohl, "The Empire and the Lombards: Treaties and Negotiations in the Sixth Century", a chapter in Kingdoms and Empire: The Integration of Barbarians in Late Antiquity, ed. Walter Pohl (Brill, 1997)
Interesting looking book length studies of Christianization during the Middle Ages:
- Varieties of Religious Conversion in the Middle Ages ed. James Muldoon (University of Florida Press, 1997) [especially 'For Force Is Not of God'? Compulsion and Conversion from Yahweh to Charlemagne by Lawrence G. Duggan]
- The Cross Goes North: Processes of Conversion in Northern Europe, AD 300-1300 ed. Martin Carver (Boydell Press, 2006) [especially Three Ages of Conversion at Kirkdale, North Yorkshire Philip Rahtz and Lorna Watts]
- The Viking Age as a Period of Religious Transformation: The Christianization of Norway from AD 560 to 1150/1200 by Sæbjørg Walaker Nordeide (not yet published)
- Lithuania Ascending: A Pagan Empire within East-Central Europe, 1295-1345 by S. C. Rowell (Cambridge Univesity Press, 1994)
- The Crusades and the Expansion of Catholic Christendom, 1000-1714, by John France (Taylor and Francis, 2005)
- History and Silence: Purge and Rehabilitation of Memory in Late Antiquity by Charles W. Hedrick, Jr. (This book doesn't really meet my official criteria for this post, since it deals with Late Antiquity instead of the Middle Ages, and I have also mentioned it many times before in this blog. But its an absolutely essential work of scholarship on the process of Christianization, and it was just reissued as a paperback in 2010, so I am giving it another plug.) (University of Texas Press, 2000)