Cannith, Mark of Making: Most prosperous of the Twelve, focused on artifice. The house is divided into three factions as a result of the Day of Mourning, as Cyre was the seat of the House.
Deneith, Mark of Sentinel: A mercenary outfit. They remained neutral during the Last War, though that is not to say they did not fight. Of late, they find themselves competing with House Tharashk, who are bringing in monstrous mercenaries from Droaam.
Orien, Mark of Passage: Caravans and couriers. They ride and patrol the roads of Khorvaire, and operate the lightning trains. Perhaps the most-civic minded house.
Lyrander, Mark of Storm: Sailors of the seas and skies. They are bold and daring, and command the elementals vessels that are a hallmark of the setting. There is a darker side to them as well, as a handful of them are keen on half-elven separatism.
Ghallanda and Jorasco, the Marks of Hospitality and Healing: Ghallanda is hoteliers, Jorasco is healers. One of them is much more assimilated into Khorvaire society, but I can’t ‘member which.
Medani, Mark of Detection: Smallest of the houses. Mostly private eyes and investigators. They tend to keep a low profile and stay out of politics.
Sivis, Mark of Scribing: Bureaucrats, scriveners, archivists, barristers, and paper-pushers in general. They are integral to the communication infrastructure of the Five Nations. Mostly innocuous, but the combination of private communications and gnomish curiosity makes for some paranoid fantasies.
Tharashk, Mark of Finding: Prospectors, bounty hunters, and trackers. Least “civilized” of the houses, least aristocratic of the houses. The half-orcs are pretty rough-and-tumble, and their outland homes allow them to make alliances with monstrous beings.
Vadalis, Mark of Handling: Animal husbandry of all varieties. The only real trouble they get into is when they try to rustle some Valenar elvish steeds.
Phiarlan and Thuranni, Mark of Shadow: A much more bitterly divided house than Cannith, the elven houses are guilds of entertainers with a knack for illusions. However, they are also rumored to be spies of tremendous cunning.
Kundarak, Mark of Warding: The Bankers of Khorvaire. These dwarves seek to build secure fortresses and holds. Their most famous is Dreadhold, a prison in the Lhazaar Principalities where the worst criminals in the world are sent.