The Cenarion Expedition is the second reputation that you will encounter when in the Outlands. The main hub of the Cenarion Expedition is located in Zangarmarsh, however there is a second in Blade's Edge. You can do quests from both areas to increase your reputation. There are also 3 instances tied to the Cenarion Expedition reputation. Those instances are Underbog, Slave Pens and Steamvaults.
Slave Pens and Underbog are lower level instances and will stop giving you reputation towards the end of honored. However Steamvaults is a high level instance and will give you reputation all the way through. Also when you're running Steamvaults you can also pick up Coilfang Armaments to increase your Cenarion Expedition rep even more.
Very similar to the Armaments in Steamvaults in Underbog you can also pick up Sanguine Hibiscus. These can be turned in at Sporeggar to increase your Sporeggar reputation.