An excerpt from the Journeyman's Guide to Daedra, Oblivion and Conjuration, by Francis Verne, Magister of Daedric Studies of the College of Whispers.

For every Daedric prince, there are a thousand Demiprinces, each one as powerful as a minor god like Xarxes or Diagna. Though they are obscure, one should not attempt to interfere in matters of Oblivion without a basic knowledge. As such, here is a list of notable Demiprinces.

The Atronach Monarchs: The Demiprinces who lead the Atronachs, the Monarchs number three per kind of Atronach, except for the Frost Monarchs, who number two due to one of their number being imprisoned in a legendary sword. Judging by this and the low status of Atronachs, they are generally agreed to be the weakest of Demiprinces.

Peryite: Although not a Demiprince, Peryite is their king. Through them he keeps the lesser Daedra in line, and despite being the weakest Daedric Prince, he is the most vital to the running of Oblivion, for he prevents the Demiprinces from growing upset and attempting to overthrow the true Princes. As such, Peryite is counted as Prince of Demiprinces.

Xalthas: This Demiprince's Sphere is cities and buildings. He is the conciousness of the minor plane "Xalthasem", which is the largest city in the Aurbis, the size of the Summerset Isles. Namira, who loathes the civilisation inherent in cities, invoked Xalthas's protonymic to cause the city to collapse. It is currently being rebuilt as Xalthas reforms in Oblivion.

Gulamorjil: This powerful Demiprince is believed to be related to Molag Bal. Despite his heritage, Gulamorjil is one of the Tribunal Temple's allies, and it is said during the Oblivion Crisis he intervened to help save Necrom.

Umbra: Umbra is the most famous of Demiprinces. His actions and history I summarize in my other work "Umbriel: The Truth Behind the Infernal City Incident". Technically, he was not a Demiprince until said incident.

Fa-Nuit-Hen: Also known as the Multiplier of Motions known, Fa-Nuit-Hen's sphere is speed and agility. It is said that the famous Khajiit Athlete S'darra got her agility from him in exchange for worshipping him. Her unfortunate paralysis that lead to her death is believed to be Fa-Nuit-Hen's curse after she forsaken Daedric Worship to follow the Nine Divines.