Barbara Yorke has written a nice summation of the current state of research into the origins of six of the seven kingdoms of the Heptarchy, the classic seven-kingdom division of England (defined as the land held by the Anglo-Saxons) in the Sixth through Eighth Centuries (the seventh, Sussex, is even more poorly documented than the others, and she treats it in the sections on Kent and Wessex). There are various ways to approach the king lists for this period, and Yorke is somewhat of a minimalist, preferring not to list rulers who cannot be attested by relatively reliable sources (and for early Anglo-Saxon England, "relatively reliable" is itself a relative term), so her lists do not include some rulers mentioned in that reliable old stand-by, the "Handbook of British Chronology." She also includes useful notes on what little is known about some of the less-known groups which may have been sub-kingdoms with brief flashes of autonomy, like Lindsey, Wight, the Hwicce, Middle Angles and Maegonsaeten, and Elmet.
Most interesting to me was her careful reconstruction of the political trajectory of Kent, suggesting that instead of being a single state, it may have been for much of its history divided into two kingdoms, East Kent and West Kent, the latter at times including Sussex, and that many of the kings listed. whose chronology has been so debateable, may in fact have ruled concurrently in its two halves.
This is a useful addition to the library of anyone interested in Anglo-Saxon England or the "Dark Ages," and a nice guide to the period that fascinated J.R.R. Tolkien and from which he drew much of Middle Earth.