The dragonmarks, in 3.5, served to make most of the core PHB races interesting again. The Dragonmarked houses are a very cool aspect of Eberron, and having a PC be torn between loyalty to his house and supporting a Prince he is dedicated to would be interesting. Were I PCing in my own game, I would almost certainly play a dragonmarked scion.
Archetype: Dragonmarked Scion
Race: Depends of House: Human, Half-Elf, Halfling, Elf, Dwarf, Gnome, or Half-Orc
Religion: Sovereign Host, Dark Six (most common); Silver Flame, Blood of Vol, Spirits of the Past (less common)
Hook: You are a member of a Dragonmarked house that has been assigned to work with Prince Oargev. Your family is among the economic elite, exercising great power and influence over certain sectors of the war-time economy.
Benefits: You automatically gain a background benefit related to your house. In addition, you select either Impressive Connections, Well-Traveled, or Superior Education.
Impressive Connections: In any sufficiently large city across Khorvaire, and anywhere in Cyre, you may roll a Streetwise, History, or Insight check to discover if there is someone in town with whome you are connected. The higher your check, the better the connection. The skill you choose to use will determine the sort of help your connection will offer (Streetwise: a merchant connection- benefits to buying and selling in town; History: a family connection- a place to stay, contacts in local society, formal introductions; Insight- Old Friends- a place to stay, contacts in regular society, active help in your affairs in-town.)
Superior Education: Choose 1: You gain +3 in one associated skill, all associated skills as class skills, +1 in three associated skills, or 2 bonus languages. Associated skills: Arcana, Diplomacy, History, Insight, and Religion. Also, you know a handful of gifted scholars and have established connections in one or more educational institutions.
Well Traveled: You gain 2 bonus languages. You may keep these languages undetermined until you decide that you should know the language in question. At that point, you may set a specific language. You may not select any secret languages as these two bonus languages. In addition, there is a decent chance you have an old friend or acquaintance in any new place you travel.AND
House Cannith (Human): You can use one additional Magic Item Daily power per day.
House Deneith (Human): You gain proficiency with all military melee weapons, any one superior weapon, or any one armor or shield (ignoring ability score prerequisites, but not other prerequisites)
House Ghallanda (Halfling): You know all about the best inns and taverns in Khorvaire. In any city, within an hour of settling in, you can get a full report on the major news of the city.
House Jorasco (Halfling): In any city, you can buy any magic item that has a daily power with the healing keyword or any ritual associated with the Heal skill for 75% of the cost.
House Kundarak (Dwarf): While in any city, you have access to short-term, intrest-free loans from the family coffers. You may borrow money up to the value of a magic item of your level. You must pay this money back before you will be allowed to borrow any more. If you pay back the loan before you gain a level, funds will become immediately available to you for another loan. For every level you gain before paying back the loan, you must level up an equal number of times before you will be able to take out a maximum loan again. You can, however, get lesser loans equal to a magic item of your level-half the number of levels you must gain before being eligible for the full amount, rounding down.
House Lyrandar (Half-Elf): You can obtain sea (or eventually air) transportation at 75% of cost. Also, in any port, you can get at least one piece of international news.
House Medani (Half-Elf): You can purchase items that grant a bonus to Insight or Perception checks, and divination rituals at 75% of cost. In addition, you can always know who the best inquisitive in any given city or town is within 30 minutes of talking to people in the town.
House Orien (Human): You can obtain over-land or teleportation transportation at 75% of cost. Also, if you can cast Teleportation Circle, you gain one additional Portal Code, and can gain an additional free portal code at every level ending with a 4 or 8.
House Phiarlan (Elf): You have access to a spy network. Each level, you may ask a question of your network. The next time you level up, at some point during that level, you will get an answer. It will be accurate, though it may be misleading.
House Sivis (Gnome): Once per level, you can get a message to anyone, anywhere, for free. You must be in a city in order to send this message.
House Tharashk (Human or Half-Orc): Your house has an agreement with magic item produces to get deep discounts on enchanted dragon-shard items. In any city, you can buy dragon-shard items at 75% of cost. Also, in any city, you can get reasonably accurate directions to any one person's home or business 10 minutes of asking.
House Thuranni (Elf): You have access to a spy network. Each level, you may ask a question of your network. The next time you level up, at some point during that level, you will get an answer. It will be accurate, though it may be misleading.
House Vadalis (Human): You gain the Mounted Combat feat for free. You can buy animals for 75% of cost.
Commentary: I decided that, if someone wanted to play a member of a dragonmarked house, they were probably going to be going for the feats and possibly even the paragon path related to the house. Those feats certainly tend to push characters certain directions, so I figured that should be the only inducement to certain classes I needed. Even though racial restrictions were removed for dragonmarks in 4ed, I am certainly keeping them as is. If you are a Dragonmarked Scion archetype, you will be playing a pretty representative member of your house to a large degree, but how you interpret your house is left pretty wide open.
Coming up with individual benefits according to house was tough, but kind of fun. I didn't want to retread the bonuses they get from dragonmark feats, but I wanted to represent the significant (largely economic) benefits to being from a dragonmarked house.
We had one player toy with this archetype before finally deciding on playing a Cyran Nobel. I breifly considered running a 4th DMPC with this archetype rather than Tact, but decided that I didn't want to bother having to run a character in addition to DMing. I will certainly flash the shiny dragonmarked houses in front of any new PCs we happen to pick up.