For its series Dune, Frank Herbert does not seek to present a model of human society innovating or surprising at the scale of the galaxy. On the contrary, the author supposes that the colonization of planets naturally brought a feudal model. Each planet is managed like a stronghold by a noble family or Major House. The Minor Houses are vassal of the Major ones.
The coherence of the unit is ensured by an emperor and countervailing powers providing of the services "of public utility": the Space Guild, having the monopoly of space transport inter-systems (through the hyperspace), the Company of Honest Ober Merchants, the equivalent of the World Organization of the Trade, and finally various organizations aiming, by a specific teaching, with the improvement of the human capacities but of which the true goals are more obscure.
In the Majipoor series of Robert Silverberg, the capacity on the giant planet Majipoor is shared between four powerful characters: the Coronal holds the executive power, the Pontiff holds the legislature, the Island Lady plays a federator part in the religious field. As for the mysterious King of the Dreams, he represents a countervailing power compared to the first three powers, and his role seems ambiguous: at the same time hated and appreciated by the population of Majipoor.
The cycle the Lords of Instrumentalité de Cordwainer Smith presents the Instrumentality of Mankind, a sort of political agency on a galactic scale, whose members put all works about it to assist progress of humanity. The Instrumentality does not have the role to replace the planetary governments; its members have capacities extended in the field of the diplomacy, of the negotiation, but they can be corrupted. Their currency appears simple: to supervise without managing, protecting without controlling.