For my second article about old world factions, I want to focus on the Cenarion Circle. The main quest hub for the Cenarion Circle is in Silithus, a level 55-60 zone in Kalimdor. Most of the items they sell are obsolete now, but for Tailors they sell two recipes for Herb Bags at Honored and Revered that have no end-game counterparts. They also sell patterns for nature resist gear, but I believe most of that has been replaced by Cenarion Expedition recipes.
Previously this faction was a bit challenging to level up once the normal zone quests ran out. The primary choices after that were to farm many mobs for drops, kill mini-bosses in the zone or run Ahn'Qiraj raids. The best non-raid options required you to farm elite mobs with a group of 3-5, not particularly solo friendly. I personally gave up at Honored because I didn't want to burden my guildies with hanging out with me night after night to kill elites.
This has changed quite a bit with the most recent patch, most of the "hive" mobs have been downgraded to non-elites, which makes the Field Duty quests viable for a solo player. They also increased the rep gains for the repeatable quests, so your faction will go up much faster than it did pre-expansion. Here's a breakdown of the repeatable tasks and the faction they give at level 70:
Field Duty (quest starter task): 50 rep
Combat/Logistic/Tactical Quest (follow-up to Field Duty): 150 rep
Abyssal Crest x 3: 150 rep
Twilight Text x 10: 500 rep
Abyssal Signet: 700 rep
For mob kills you get 2 points per Twilight Avenger and 0 points per Twilight Geolord. To collect the Abyssal Crests for the turn-in quest you need to kill Abyssal Templars, which are summoned using the lesser wind stones at the Twilight Camps and donning the Twilight outfits that are dropped by the Twilight mobs in the area. You can also purchase Twilight gear off the auction if you prefer, there are usually some up for about 1g per piece. For an Abyssal Signet, you need to kill the Abyssal Dukes which are summoned by the regular wind stones at the Twilight camp, while wearing the Twilight gear. Each Duke will give you 50 rep for the kill in addition to the rep from turning in the quest.
If you are level 70 and working on your rep, the exciting part is that you can now solo the Abyssal Templars and Dukes. They are still elite mobs, but being level 60 they don't pose a challenge. I had no trouble at all killing the Templars, and minimal difficulty with the Dukes. I was able to solo them while wearing my DPS gear in bear form. I didn't attempt an Abyssal Lord, the hardest of the summoned bosses, but that might also be workable for the right class. I felt the Dukes were challenging enough since they require 3 Abyssal Crests (from the Templars) + 1 Twilight outfit + 1 Large Brilliant Shard to summon. You end up with 750 rep from the kill + quest, but the component cost is quite high. So some folks may prefer to stick with the Templars, which only require a Twilight outfit to summon.
From my experience, the quickest way to increase rep is by killing the Dukes. If you hang around the Twilight camps, it's fairly easy to kill the various Twilight humans, collect Twilight pages as well as the Twilight outfits needed to summon an Abyssal boss. I think it's quite reasonable to get at least 1000 rep an hour if you work the camp for the materials for a Duke and then summon one, kill it and turn in the quest. The only item you'd have to supply yourself would be the Large Brilliant Shard if you want to minimize your costs.
It would take even less time if you purchased all the outfits ahead of time, but you'd spend about 3g per summon doing it that way. Since you need to summon four times for the Duke, that would run you about 12g in outfits, plus the shard being another 5-10g. Even this route isn't terribly expensive in terms of costs/rep gained, so it's up to you how you want to work it.
For folks who prefer not to deal with the Abyssal summoning, running Field Duty quests is also an option. By doing each of the three different types of tasks, you can get one of each badge type. Turning in a set of three badges will give you 500 rep, in addition to the 150 rep you got from each quest to earn a badge and the 50 rep each time you do Field Duty. One of the badge types requires doing a crafting task, so you'd probably want to be sure you had the materials on hand before you go this route. It would surely increase the annoyance factor if you had to farm the components for old-world items. But this is another option that would probably take around an hour and net about 1100 rep.
If you are completely unfamiliar with the Cenarion Circle, most of this probably sounds confusing. Admittedly, this process is more complex than most other factions. For a full rundown of the various quests, visit the WowWiki page.