Factions of Northrend at a Glance

Blizzard made some great changes to factions in the Wrath of the Lich King expansion. It's no longer required to grind faction in specific instances to get enough repuation to buy items from their respective quartermasters. Instead Blizzard implemented a system where you buy a tabbard for the faction and gain rep from running dungeons while wearing the tabbard. This works for all level 80 dungeons (Occulus, Caverns of Time, Utgarde Pinnacle, and Halls of Lightning) as well as all heroic dungeons. So where do we buy these elusive tabbards? They can be purchased for 1 gold from the respective faction quartermasters, however, you must obtain friendly status with the faction first. You can also gain faction from doing daily and non-daily quests as well as completing the daily dungeon quest available in Dalaran. The reward for completion of this quest is your choice of a faction specific commendation token which earns you reputation.

The following is some information for those of you just starting out in building reputation with the Northrend factions.

Argent Crusade
Primary base with quartermaster is located at the Argent Vangaurd in Icecrown.
There are two daily quests which can be used to build reputation with the faction:
http://www.wowwiki.com/Quest:Pa%27Troll and http://www.wowwiki.com/Quest:Slaves_to_Saronite
There are numerous non-daily quests through out Howling Fjord, Dragonblight, Zul'Drak, and Icecrown.
The Argent Crusade quartermaster sells a head enchant to those Revered with their faction. This head enchant gives +37 stamina and +20 defense.

Kirin Tor
Primary base with quartermaster is located in the Violet Citadel in Dalaran (look for the giant staircase in the corner of Dalaran, you can't miss it!)
Reputation can be earned by doing the daily fishing, cooking, jewelcrafting and the two daily dungeon quests (regular and heroic).
Non-daily quests can be found in Borean Tundra, Coldarra, Dragonblight and Dalaran.
The Kirin Tor quartermaster also offers a head enchant at revered. This enchant provides +30 spellpower and +20 crit rating.

Knights of the Ebon Blade
You can find their quartermaster at the Shadow Vault in Icecrown, but there is a catch! If you are not a Death Knight, you must complete the quest chain that begins with http://www.wowwiki.com/Quest:It%27s_All_Fun_and_Games in order to phase the vault to where you will have merchants, flight paths and such accessible (that means you have to do the chain to get the quartermaster to buy the tabbard!)
The Ebon Blade have 3 daily quests available at the Shadow Vault and 2 more at Death's Rise.
Zul'Drak and Icecrown each offer several quest hubs with non-daily Ebon Blade quests.
Like the other factions, the Ebon Blade offers a head enchant which gives +50 attack power and +20 crit rating.

Wyrmrest Accord
At the very top of the Wyrmrest Temple in Dragonblight, you will find the quartermaster for the Wyrmrest Accord.
Two dailies can be found in Coldarra along with one in Dragonblight.
Various non-daily quests can be picked up at the Temple in Dragonblight.
Wyrmrest's head enchant offers +30 spellpower and +8mp5.