Thirteen families carry dragonmarks (twelve houses, since Phiarlan and Thuranni share one mark). Together with Kundarak’s banks and Sivis’s messengers, they are the economy. A dragonmark gives its bearer spells tied to the house’s trade. Siberys marks are rare, huge versions of a mark. Aberrant marks belong to no house and are distrusted.

HouseMarkRaceBusiness
CannithMakingHumanMagic items, warforged (formerly), industry. Leaderless since its patriarch died in Cyre; split into Cannith East, West and South.
DeneithSentinelHumanBodyguards (Defenders Guild), mercenaries (Blademarks), and the Sentinel Marshals, who can make arrests across national borders
GhallandaHospitalityHalflingInns, food, safe houses
JorascoHealingHalflingHealing houses (for a fee)
KundarakWardingDwarfBanks, vaults, letters of credit
LyrandarStormHalf-elfAirships, sea trade, weather control
MedaniDetectionHalf-elfInquisitives, bodyguard screening, poison detection
OrienPassageHumanLightning rail, couriers, caravans, teleportation
PhiarlanShadowElfEntertainers and artists. Everyone knows it’s also espionage
ThuranniShadowElfSplit from Phiarlan in 972 YK’s bloody Shadow Schism. Entertainment, espionage, assassination
SivisScribingGnomeTranslation, notaries, speaking-stone message stations
TharashkFindingHuman / half-orcBounty hunters, inquisitives, dragonshard prospectors
VadalisHandlingHumanMagebred animals: horses, hippogriffs, war beasts

From the Eberron Player Primer. Public knowledge and rumour only.