FIRST check the prices of both elemental water and essence of water on your server. If they are low, this guide isn't for you.
Otherwise, read on:
Go to this NPC.
Alliance: Arathandris Silversky - NPC - World of Warcraft
Horde: Maybess Riverbreeze - NPC - World of Warcraft
Complete the quest "Cleansing Felwood".
This will unlock all of the cenarion plant salve quests.
Now, go up to northern felwood. Grind these elementals for as long as you desire: Toxic Horror - NPC - World of Warcraft
Lots of good drops... Argent Dawn rep items, elemental water, essence of water, greens, and blues. The respawn timer on these guys is fairly quick. Just find a route that works for you and start getting some gold!
Not to mention, all of the kills will give you Corrupted Soul Shards. Corrupted soul shards can be turned into the NPC I spoke of above, in exchange for cenarion plant salve. Cenarion plant salve can be used on the plants of felwood to get buffs, food, etc.
This is how I decided to level from 51-55. Flame me if you wish. I'm just trying to help out my fellow mmowners =D