Easy Leveling 20-25 In Butcherblock
There is a quest you can obtain from NPC Talvrae T'Zyth by the Greater Faydark entrance called "A mind of my own". Quest ID is 4131 on allakhazam.
Basically she wants you to place a bowl in front of a kobold type creature (the Yarpsnarls), and this will charm it, she wants you to have it fight other yarpsnarls and kill 12 of them.
However the first part of this exploit is that after you charm a Yarpsnarl you can have it attack whatever you want and if it's not another Yarpsnarl it won't count against the quest.
The biggest part of this exploit is that normally Yarpsnarl Mystics do around 50ish damage when they nuke you, however if you charm one they nuke for upwards of about 700-800 on other mobs. They can sometimes crit for over 1k damage.
As a shadowknight around level 22 I was jumping in to groups of 3 yarpsnarls in the camps near by with little or no downtime between killing because of how awesome the mystic is. And the best part about it is after your pet dies you can go request another bowl from her, or if you complete the quest you can just delete it before talking to her again and start the quest over.
you can charm the higher level 34ish Yarpsnarls with the bowl too. They are too high though and you won't receive any experience for what they kill.