The Horde 12-20 (Barrens + Stonetalon Mountains) guide has been rewritten and revamped.  In addition, there has been numerous tweaks to the speedrun route to make things faster and easier to follow.  Also, in case you haven't noticed I am now adding about 40% more info per step and redoing all the images.  Unlike with my previous vanilla guides, I am now giving a brief explanation of where to go and what to do with each step along with any other helpful tips.

Regardless of how good Sulfuras actually was, if you ever saw anyone wielding it throughout all of Vanilla, you know that was either one very dedicated person, or someone that the entire guild helped get the weapon. Sulfuras doesn't actually drop directly off Ragnaros - instead,  Eye of Sulfuras drops from him and you then need to go through a very long crafting process so you can use the Eye to convert your crafted Sulfuron Hammer into it's final form: Sulfuras, Hand of Ragnaros.
Haste is a stat not thought by many to be very useful to priests. However, while leveling, a priest’s primary source of damage will be their wand, and Haste affects a wand’s attack speed, which means more DPS. There are very few effects that will grant haste, though. In fact, the only reasonable one I can think of is the enchant to gloves. If there is enough money in the bags to toss an enchant on a decent pair of gloves, be sure to ask for Haste.
The second issue is distinguishing the difference between DPS (damage per second) and DPM (damage per mana). While leveling, one wants to be efficient, which most people interpret as “kill stuff as fast as possible.” What being efficient actually means is earning as much experience per hour as possible. Priests can kill things really fast, but if one spends twenty seconds drinking after every kill or two, one is not being very efficient.
Swim Speed Potions (used especially at lvl 37 for Faldir's Cove in Arathi Highlands and lvl 57 in WPL).  Try to get multiple stacks of these.  I also recommend keeping a stack of these always in your bags.  You will frequently pass rivers and lakes and can use these potions to pass them faster through out the guide.  Please note that these potions do not stack with Druid's Aquatic Form and Glyph of Aquatic Form.
This Addon solves that issue where you have 5 Paladins in your Raid and no one can decide who is Buffing what. It has a little UI that represents Different Classes in your Party or Raid. You can change what buffs you want to give out then just mash the Class Button for each Class type until they all Turn Green. If anyone is missing a buff you are assigned the Class