Updated Sun, Feb 24, 2008 by DarkFact
The Cenarion Expedition's HQ is within Zangarmarsh and is the first neutral town you arrive to once you reach this level 62 zone. While you will have met the Cenarion Expedition before in Hellfire Peninsula's outpost near the exit to Zangarmarsh, this will be your real initial contact with them. Cenarion Expedition reputation is required for you to access the Coilfang Reservoir's heroic mode dungeons, along with random goodies for healers mostly. You may visit their quartermaster infront of the Inn at the Cenarion Refuge.
From World of Warcraft's site,
The Cenarion Circle's main expeditionary force in Outland is known as the Cenarion Expedition. Though it began as a small venture controlled directly by the Cenarion Circle, the expedition has become a large and fairly autonomous body. The expedition is based at Cenarion Refuge in the far east of Zangarmarsh, immediately west of Thornfang Hill in Hellfire Peninsula.
The druids' original goal in coming to Zangarmarsh was to study the rich wildlife there, but the group has discovered troubling goings-on in the marsh. Water levels in many parts of Zangarmarsh are decreasing, and some areas such as the Dead Mire have already suffered greatly from this strange phenomenon.
The druids of the Cenarion Refuge believe that the naga are to blame, but the Expedition cannot afford a direct confrontation with the many naga in Zangarmarsh and Coilfang Reservoir. The Cenarion Expedition needs the aid of adventurers willing to assist the druids in their dangerous fight against those who seek to disturb the marsh's natural balance. Anyone brave enough to combat the naga at Coilfang Reservoir will be well rewarded.
As with Thrallmar and Honor Hold, it is recommended you kill Naga in the area so you bump up your reputation some, to atleast halfway through Neutral before attempting any quests involving the Cenarion Hold, by doing this you allow your reputation to have an advantage and hopefully minimize the reputation grinding you will be needing to do in the end!
Monsters that will yield reputation for you as you fight in Zangarmarsh if you're neutral are:
There's many ways to be Honored quickly with the Cenarion Expedition - you may run Slave Pens and Underbog, complete the quests within (or save the completed quest), earning 7 reputation per kill and 70 reputation per boss kill.
In addition to quests, (if you complete them all, you should be earning around 16,000 reputation, including the Dungeon quests and quests in all zones), you will have the option to do the quest "Plants of Zangarmarsh"
Bring 10 Unidentified Plant Parts to Lauranna Thar'well at the Cenarion Refuge in Zangarmarsh.
This quest will get you 250 reputation points with the Cenarion Expedition in addition to a bag of consumables, herbs and other items, and will take you to Honored, so it's a nice addition to grinding Naga enemies.
You will be finding yourself unable to keep obtaining Reputation once you hit Honored from anything but quests once you hit Honored, so it's in your best interest to turn in your uncatalogued species now all together for a good boost in your reputation bar.
Afterwards, you won't have much choice but to hit level 69 or 70 and hit the SteamVault dungeon, this dungeon will be giving you around 1662 reputation for a full clear, and you will be getting Coilfang Armaments, which can be redeemed with a quest you obtain from a random kill, "Orders from Lady Vashj", for 75 reputation a piece (250 initial reputation).
As usual, you will have 2 choices if you're gunning for Exalted, run the Heroic versions of the dungeons for reputation per kill, or run normal Steamvaults for normal reputation gain (yet easier), remember that Steamvault will yield Coilfang Armaments randomly for turn-ins!
Numbers are only available for Steamvault
Steamvault - Normal (Neutral ~ Exalted) = ~1660 reputation per run
Steamvault - Heroic (Revered ~ Exalted) = ~1660 reputation per run
As you can see, it won't vary much, so your best bet for a quick Exalted will be running Heroic versions of Underbog and Slave Pens due to the sheer amount of monsters you kill in both, and how they each yield 4-6 reputation per kill in Heroic mode!