The Wrath of the Lich King expansion added several new factions to World of Warcraft, and it has also given players a new method of earning reputation called "championing." Here are some pointers for getting reputation rewards in Northrend

Alliance Vanguard - Rewards
The Alliance Vanguard is made up of four subfactions, each of which is connected to your Alliance Vanguard reputationThere are the Explorers' League, The Frostborn, The Silver Covenant, and the Valiance ExpeditionThere are no item rewards for the subfactions, but any reputation gained with a subfaction also increases your Alliance Vanguard reputation

Horde Expedition - Rewards
The Horde Expedition also consists of 4 subfactions: The Hand of Vengeance, The Sunreavers, The Taunka, and the Warsong OffensiveThe Horde Expedition is led by Garrosh Hellscream in Warsong Hold, and that's also where you find the QuartermasterEarning reputation for any of the subfactions contributes to your overall Horde Expedition standing

Kalu'ak - Rewards
This tribe of walrus-like tuskarr has two Quartermasters in NorthrendOne is Sairuk at Moa'ki Harbor in Dragonblight, the other is Tanaika at Kamagua in Howling Fjord

Sons of Hodir - Rewards
Based in Dun Niffelem in the Storm Peaks zone, the Sons of Hodir are frost giants that start out as aggressive to playersTo gain neutral standing with them you need to do the quest chain that begins with "They Took Our Men!" in K3Most of the rewards for Sons of Hodir reputation are shoulder augmentations

Sholazar Basin
There are two factions with which you can align yourself in the Sholazar Basin zoneThese are the opposing Frenzyheart Tribe and the OraclesGaining reputation with one will make you an enemy of the otherYou align yourself by completing along quest chain which includes "A Hero's Burden." If you kill Zepik during this quest you become aligned with the Oracles, if you kill Jaloot you become aligned with the Frenzyheart Tribe

Frenzyheart Tribe - Rewards
Oracles - Rewards

Championing
"Championing" is a new way to gain reputation in Wrath of the Lich KingBy wearing the tabard of a particular faction while doing level 80 or Heroic Northrend dungeons, you gain reputation for that factionTabards are available from the faction Quartermasters once you are friendly with the factionThe following 4 factions are those to which championing applies

Argent Crusade - Rewards
Born from the union of the Argent Dawn and the Order of the Silver Hand, the Argent Crusade was formed to fight against the Lich King in NorthrendThe primary base for the Argent Crusade is the Argent Vanguard in Icecrown, right near the border with DragonblightThis is where you will find the QuartermasterThere are other encampments in Dragonblight and Zul'Drak

Kirin Tor - Rewards
The Kirin Tor is a powerful sect of mages based in the city of DalaranThe Quartermaster is in the Violet Citadel

Knights of the Ebon Blade - Rewards
A group of renegade Death Knights, the Knights of the Ebon Blade are based in The Ebon Hold in Eastern PlaguelandsIn Northrend, their main encampment is the Shadow Vault in Icecrown, which is where the Quartermaster isNote that the Shadow Vault encampment only appears after completing certain quests in IcecrownThe also have a camp at the Ebon Watch in Zul'Drak