Some good places are: Eastern Kingdoms (North): Loch Modan: The excavation site Wetlands: Any area that has Mosshide Gnolls Silverpine Forest: Fenris Island's undead gnolls (can't remember their name) Eastern Kingdoms (South): Redridge Mountains: Any area that has Blackrock Orcs.
(Alliance only)
Stormwind City:
The Stockade dungeon...
of course, all enemies in it are elites.
Kalimdor: Ashenvale Forest:
The Naga near Blackfathom Deeps...
and if you're high enough level, Blackfathom Deeps itself...
of course, all enemies in it are elites.
The Barrens: Any area that has Razormanes, particularly the ones outside RFK and RFD.
NOTE:
We're at most a month away from The Shattering (the part of Cataclysm that changes the world), so these locations may no longer be there or change their level spread/drop rates after it happens.
gaming.stackexchange.com/users/None/
The easiest way to figure out where to farm an item is to have a look at the item's drop rates in Wowhead and find the mobs with the highest drop rate but also a large number of spawn points.
In this case, I had a look at the Wool Cloth page and found two good areas:
There's a cave in Stonetalon Mountains that may be good, with Windshear Stonecutter , Windshear Vermin and Windshear Overlord all having good drop rates but not many spawn points.
Durnholde Keep in Hillsbrad Foothills seems to be the best choice, with a good drop rate from Syndicate Watchman and Syndicate Rogue and 100s of them available to kill.
gaming.stackexchange.com/users/4584/dlanod
Recently I needed to get my tailoring skill up on my level 30 undead warrior.
Fenris Island worked out pretty well for getting wool cloth.
gaming.stackexchange.com/users/664/projecktzero
Also check thottbot.com .
It has maps with drop info and percentages from mobs that may be of use.
You can use ThottBot for lots of stuff like this.
gaming.stackexchange.com/users/3291/angryITguy
This isn't a direct answer to your question, but the best place to farm wool cloth would be whatever place earns you the highest amount of gold per hour, which you can spend at the auction house to purchase wool cloth.
This ensures you are making the most of your time .
Here's an example to illustrate.
(Note that these numbers are entirely made up )
Say the current going rate of a stack of wool cloth on the auction house is 20g.
You can either: Spend 30 minutes killing humanoids in Shadowfang Keep for 1 stack of wool cloth (worth 20g), or Spend 30 minutes killing Lesser Pantaloon Demons in the Emerald Dream for half a stack of Primal Cheese (worth 50g, which can buy 2.5 stacks of wool cloth!)
gaming.stackexchange.com/users/274/Brant
The best place for farming wool is Dawning Woods Catacombs in Ravenhill, Duskwood.
There are 2 entrances to the crypts, both underground areas.
You want the one in the West, which is guarded by a giant skele.
Kill giant skele, descend to first level-
kill everything and loot.
Go to 2nd level, and only kill what is in the hallway.
Kill left room, kill right room, then go out, and do again.
If you kill the hovering boss, everything dies in the crypt leaving them unlootable!
gaming.stackexchange.com/users/16677/Farmer John
If you have a level 80 (or even a 60+), the easiest way to farm wool is at Shadowfang Keep.
The real trick to making gold off of the wool is to know how much to put it up for at the AH.
Put too much up and you'll drive prices down due to the fact that the economy only demands so much of it over a certain period of time.
But I digress from your original question...
gaming.stackexchange.com/users/4737/Jagd
Before
The Shattering , I would have pointed you to the Deadmines.
Now post Cataclysm , I believe Shadowfang Keep is great place to farm for wool.
It's quick and easy.
Furthermore there is no competing with another players for the same resource when in an instant by yourself.
Notice, I didn't say best .
For the most part, considering a place the 'best' for [whatever], is a matter of opinion.
Good luck and happy hunting!
gaming.stackexchange.com/users/4989/SgtOJ
In my server the price for Wool Cloth in the Auction House is very high, considering it's a low level item. What's the best place to farm it?
Where is the best place to farm for Wool Cloth?
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gaming.stackexchange.com/questions/10522
gaming.stackexchange.com/users/2715/Farinha
Shadowfang Keep, Eastern Kingdoms, any area that has Mosshide Gnolls and Blackrock orcs. There are a number of locations where this can be done, Shadowfang Keep chief among them, Loch Modan, Mosshide Gnolls and others. There is not really a specific answer to this, the best place would be the place with the best rates. Another option is to use external software like Wowhead to help you. 
Users suggest locations where this can be done. User vaguely says that the amount of gold per hour is what counts. A user also suggests using external software that will tell you the rates.