The Heroic modes of all dungeons in Outland require a key for access. Acquiring the key for each dungeon area requires Revered reputation with a specific faction. The key can be purchased from the corresponding faction Quartermaster.

The Burning Crusade Faction and Reputation Overview
The Heroic modes of all dungeons in Outland require a key for access. Acquiring the key for each dungeon area requires Revered reputation with a specific faction. The key can be purchased from the corresponding faction Quartermaster.
The Reputation Interface
The default key for opening the Reputation interface is u. The same interface can also be opened by clicking the middle tab at the bottom of the Character interface, default key c. The Burning Crusade Reputations can be found by scrolling down the Reputations list to The Burning Crusade. Some factions will not be added to the interface until they are encountered during gameplay.
The Reputation Bar for each faction indicates your current standing with that faction. Hovering over a Reputation bar will display how many Reputation Points you have with that faction, and how many you need to acquire to reach the next level. Clicking on a reputation will open a small interface with a brief Reputation description and three checkbox options.

At War: When checked, this allows you to attack members of that faction if they are not already hostile toward you. Killing members of a faction will reduce your standing with them.
Move to Inactive: When checked, the Reputation Bar is removed from the list under its expansion, and added to an Inactive list at the very bottom of the Reputations list.
Show as Experience Bar: When checked, this adds the Reputation bar to your User Interface directly above your Experience Bar.
Dungeon Reputations
Instance Attunement
The Heroic modes of all dungeons in Outland require a key for access. Acquiring the key for each dungeon area requires Revered reputation with a specific faction. The key can be purchased from the corresponding faction Quartermaster.

Honor Hold
Honor Hold is the Alliance outpost in Hellfire Peninsula. Honor Hold reputation is obtainable by Alliance characters only.
Revered reputation with Honor Hold is required for attunement to Heroic Hellfire Citadel dungeons for Alliance players.
Gaining Reputation
Reputation for Honor Hold is acquired by running the Hellfire Ramparts, The Blood Furnace, and The Shattered Halls dungeons as well as completing quests and killing mobs in and around Hellfire Citadel.
Reputation Rewards
Notable rewards include the  Honor Hold Tabard available for purchase from Logistics Officer Ulrike at Exalted.

Thrallmar
Thrallmar is the Horde outpost in Hellfire Peninsula. Thrallmar reputation is obtainable by Horde characters only.
Revered reputation with Thrallmar is required for attunement to Heroic Hellfire Citadel dungeons for Horde players.
Gaining Reputation
Reputation for Thrallmar is acquired by running the Hellfire Ramparts, The Blood Furnace, and The Shattered Halls dungeons as well as completing quests and killing mobs in and around Hellfire Citadel.
Reputation Rewards
Notable rewards include the  Thrallmar Tabard available for purchase at Exalted.

Cenarion Expedition
The Cenarion Expedition is a Neutral coalition of night elf and tauren forces formed by Cenarion Circle to explore beyond the Dark Portal. While they have a presence in most of the Burning Crusade zones, their base of operations is at Cenarion Refuge in Zangarmarsh.
Revered reputation with Cenarion Expedition is required for attunement to Heroic Coilfang Reservoir dungeons.
Gaining Reputation
Cenarion Expedition reputation is earned by running the The Slave Pens, The Underbog, and The Steamvault dungeons as well as completing quests and collecting  Unidentified Plant Parts and  Uncatalogued Species for turn in.
Reputation Rewards
Notable rewards are the  Cenarion War Hippogryph mount and the  Cenarion Expedition Tabard available for purchase from Fedryen Swiftspear.

Lower City
Lower City is a faction cobbled together with refugees, traders, and artisans in Shattrath City, Terokkar Forest. The Marketplace is a goldmine for strange knick-knacks, exotic food, and unique recipes. Professions trainers, Battlemasters, and the World's End Tavern can be found here.
Revered reputation with Lower City is required for attunement to Heroic Auchindoun dungeons.
Gaining Reputation
Gaining reputation with Lower City requires running Auchenai Crypts, Sethekk Halls, and Shadow Labyrinth as well as completing quests and collecting  Arakkoa Feather for turn in.
Reputation Rewards
Notable rewards include  Lower City Tabard available for purchase at Exalted, as well as Class set pieces available at Honored.

The Sha'tar
The Sha'tar are a faction of Naaru who rebuilt Shattrath City with the aid of The Aldor after its destruction by Orcs prior to the First War. Both The Aldor and The Scryers are allied with the Sha'tar. The Sha'tar are based in Shattrath City, Terokkar Forest.
Revered reputation with The Sha'tar is required for attunement to Heroic Tempest Keep dungeons.
Gaining Reputation
Reputation with the Sha'tar is earned automatically by gaining reputation with either The Aldor or The Scryers. Reaching Exalted will also require completing quests and running The Botanica, The Arcatraz, and The Mechanar.
Reputation Rewards
Notable rewards include  Sha'tar Tabard available for purchase at Exalted. Profession patterns can be purchased starting at Friendly, and Class set pieces are available at Honored.

Keepers of Time
The Keepers of Time are members of the Bronze Dragonflight charged with watching over the Caverns of Time in Tanaris. Their leaders are Andormu and Nozari.
Revered reputation with Keepers of Time is required for attunement to Heroic Caverns of Time dungeons.
Gaining Reputation
The majority of Keepers of Time reputation is earned by running the The Black Morass and Old Hillsbrad Foothills dungeons.
Reputation Rewards
Notable rewards include  Keepers of Time Tabard available for purchase at Exalted.

The Aldor
The Aldor are a faction of draenei priests who are based in Shattrath City, Terokkar Forest. They revere the Naaru and are allied with The Sha'tar in their battle against Illidan Stormrage. The Aldor are opposed to The Scryers. Players will be given the option to ally with either the Aldor or the Scryers. Declaring allegiance to one of the factions grants access to their area of Shattrath, their bank, and quests and rewards associated with the 
faction. It also puts the character in opposition with the opposing faction. Reputation gains with one are reputation losses with the other.
Gaining Reputation
Reputation with the Aldor is earned through completing quests, and collecting  Mark of Kil'jaeden,  Mark of Sargeras, and  Fel Armament for turn in.
Reputation Rewards
Notable rewards include  Aldor Tabard available for purchase at Exalted from Quartermaster Endarin who also sells gear and a variety of profession patterns starting at Friendly. At Honored, Inscriber Saalyn will sell gear enchants.

The Scryers

The Scryers are a faction of Blood Elves who are based in Shattrath City, Terokkar Forest. They oppose Kael'thas Sunstrider and are assisting the naaru against Kael'thas Sunstrider and Illidan Stormrage. The Scryers are opposed to The Aldor. Players will be given the option to ally with either the Aldor or the Scryers. Declaring allegiance to one of the factions grants access to their area of Shattrath, their bank, and quests and rewards associated with 
the faction. It also puts the character in opposition with the opposing faction. Reputation gains with one are reputation losses with the other.
Gaining Reputation
Reputation with the Scryers is earned through completing quests, and collecting  Firewing Signet,  Sunfury Signet, and  Arcane Tome for turn in.
Reputation Rewards
Notable rewards include  Scryers Tabard available for purchase at Exalted from Quartermaster Enuril who also sells gear and a variety of profession patterns starting at Friendly. Starting at Honored, Inscriber Veredis will sell gear enchants.