When you are at level 40-50 as a Warlock in World of Warcraft, where can you farm as much mobs as possible?

The Vilebranch Troll mobs in the Hinterlands are supposed to be the best farm mob. They range from level 42 to level 50 and there are several elite types. And the biggest WOW money maker the drop is "Wildvine".

"Wildvine" is used for Wildvine Potions 'Restores 1 to 1000 health and 1 to 1000 mana'. It's used by engineers, tailors, and leatherworks and required to complete the Leatherworking Wild Leather work quest (two of them).

The Auction House fee is only 30c WOW Money, therefore, there is very little risk and a stack of 20 Wildvines can sell for 5 WOW gold easily.

From the trolls you also get:

Troll Necklaces: A repeatable quest that gives you 390xp at level 44 for over 5 of them you turn in. (Alliance)
Mageweave
Silk
Silver
Flask of Mojo (used for 4 different recipes and an item for a couple of quests)

When you have got several World of Warcraft money making drops with the Wildvine possibly netting you 5 WOW Gold an hour alone. And if you are part of the Alliance - the NPC right at the Aerie Park entrance give you around 390xp for every 5 troll necklaces you turn in.