In Silithus, you’ll find Air Elementals which constantly drop Essence of Air. This is the only place in the game where this drops, and makes it worth farming. Although they range in level from 56-59, you should only kill one at a time, no matter what level you are. But, they drop the following items which can all earn you some great gold on the AH: Elemental Air – 24s each, Breath of Wind – 1-2g each, and Essence of Air – 25g each. Sometimes the don’t drop a thing, so you might have to kill a few before you see the goods, but it’s worth it.
While you’re in Silithus, there is always the Scorpids for grinding. These mobs are all over the game, but the best place for Glowing Scorpid Blood to drop is in Silithus. This loot is good for a quest at the Darkmoon Faire, and the best part is, you can turn in as many as you want and still earn tickets for them. You can generally farm these and then sell them on the AH for 1-2g each, not per stack, but per item. The only thing is that you have to be careful when pulling these, as sometimes you can pull more than one and they can overwhelm you easily that way. You will double your income with these if you are a skinner, as they always have rugged leather or Scorpid scales. Occasionally, you’ll get a great drop off of these, but it’s pretty rare.
Also in Silithus, you’ll find the Twilight Cultists. These mobs range in the high 50’s to 60, and drop Twilight Texts at about 15-20 per hour. You can normally sell these on the AH for 1-2g each, and selling them in stacks of 10 will help to increase your sales as these are used for a quest in Cenarion Hold. These mobs also drop money, some vendor loot, the occational green, and also Twilight Cultist gear, which generally goes for between 1-2g each.