Before The Taken King, the following factions allowed you to gain reputation to purchase new weapons and equipment:
Vanguard, Crucible, Dead Orbit, Future War Cult, New Monarchy, Crota's Bane, Queen's Wrath, House of Judgement, and Iron Banner
After The Taken King was released, the lonesome vendor that nobody ever visits, the Gunsmith, now has reputation. However he does not possess any items that are purchasable through increasing your rank.
Does anybody know what the reputation for the Gunsmith will be used for?
My only speculation is that it would be similar to the Cryptarch where you obtain additional items for each rank after rank 3.