Among the authoritative works on the period, the best biography of Edward the Confessor, and the most scholarly account of his reign, is by Frank Barlow, Edward the Confessor (new edition, 1997). This work is obviously important for Harold and for the domestic background of the Conquest.
D.C. Douglas, William the Conqueror (1964), is the standard biography by a scholar who devoted a lifetime's work to the Norman Conquest and Domesday studies. It is sometimes heavy going but essential for serious study of the political background.
Despite its age, F.M. Stenton, Anglo-Saxon England (third edition, 1971), remains the most important single book on the background of Anglo-Saxon history. It contains useful chapters both on the Conquest and Domesday.
Robert Bartlett, England under the Norman and Angevin kings, 1075-1225, is valuable for the political background of the Conqueror's reign and on many social and economic aspects of the Domesday record.
Sten Körner, The battle of Hastings, England, and Europe, 1035-1066 (1964), provides a detailed analysis of both the sources and the events of the period preceding the Conquest.
Finally, E.A. Freeman, A history of the Norman Conquest (third edition, 1877-79), though now antiquated in many respects, is a mine of esoteric information, much of it about Domesday Book and the major landowners named there.