You might be interested in our book list page for the Middle Ages. The books are generally overviews, either of the period as a whole or of a specific topic within the period as a whole.

It's worth pointing out that "The Dark Ages" really isn't an academically viable term any more.

I'd recommend: Charles-Edwards, After Rome

Bartlett, The Making of Europe

Stenton, Anglo-Saxon England

Higham, The Anglo-Saxon World

Davies, W., Wales in the Early Middle Ages

Davies, R.R., Domination and Conquest

Brown and Farr, Mercia: An Anglo-Saxon Kingdom in Europe

Whitelock's translation of The Anglo-Saxon Chronicle

Whitelock's English Medieval Documents, Vol. 1

Keynes and Lapidge's translation of Asser's Vita Ælfredi

Bede's Historia Ecclesiastica

Gildas, de Excidio Britanniae

The Exeter Book

Dumville's translation of the Annales Cambriae and the Brut Y Tywysogion

Dumville and Blackburn, Kings, Currency and Alliances

Lavelle, Alfred's Wars

Lavelle, The Danes in Wessex

Naismith, Early Medieval Monetary History

Naismith Citadel of the Saxons

Molyneaux, The Formation of the Kingdom of the English in the Tenth Century

Baker, Brookes, et al, Beyond the Burghal Hidage

Baker, Brookes and Reynolds, Landscapes of Defence

Stafford, Queens, Concubines and Dowagers

Stafford, After Alfred

Roach, Æthelred the Unready

McClean (ed.), History and Politics in Late Carolingian and Ottonian Europe: The Chronicle of Regino of Prüm and Adalbert of Magdeburg

Warner, Ottonian Germany: The Chronicon of Thietmar of Merseburg

That's for starters on England woth some contemporary primary sources for European context at the end.