I have been searching for books or journal articles that discuss important families and their influence on power in the medieval period. I have found many interesting sources but they are all in foreign languages and have not found translation. Most of these have been genealogical studies. I am really interested in finding out the origins of these families, how they achieved their power, and their history. It does not have to be specifically to a royal house and would actually prefer if it wasn't solely about royals.
I have seen a few documentaries from the BBC about the Plantagenets, Windsor and the Tudors. I would prefer to read about other European regions such as the low countries, France, the Iberian peninsula (and the dynastic politics of marriage to form Spain), nobles within the Holy Roman Empire, Byzantium and the Italian states.
Cecilia Gaposchkin has an excellent book called The Making of Saint Louis on the Capetians (especially Philip the Fair) and how they constructed an idea of Saint Louis (Louis IX) which promoted the dynasty.
Also in France, see Rosamond McKitterick's Charlemagne, which will give you a pretty solid basis for the Carolingians. You can look at Ganshof's The Carolingians and the Franksih Monarchy as well.
Thomas Madden's Enrico Dandolo and the Rise of Venice is quite good as well, on one of the great Venetian families around the time of the Fourth Crusade.
If you aren't opposed to rather dry political/administrative history, Bernard Reilly has quite a bit on the rulers of Leon-Castilla. He has three books on The Kingdom of Leon-Castilla Under Alfonso VI, Queen Urraca, and Alfonso VII. Simon Doubleday's The Lara Family also deals with one of northern Spain's noble families. If you're interested in Islamic Spain, there are lots of books that deal with those leaders as well.