There's a trinket in the game called Tears of Bitter Anguish.
Tears of Bitter Anguish - Item - World of Warcraft
This is only dropped by this mob - Nascent Val'kyr
Nascent Val'kyr - NPC - World of Warcraft
The Nascent Val'kyr's drop Dissolved Soul Essence
http://www.wowhead.com/?item=43574 and other BOE trash.
These Soul Essences in stacks of 20 sell for 13g60c
So for every 20 you kill, you get 13g...these guys drop FAST & EASY.
Also, the trinket sells in the upwards for 5k+...since only a few people actually have / know this trinket exists...at least on my server
Hope this helps!