My alt, currently lvl 31 NE hunter, has skinning 225 and I will have to spend 5g to be able to get my skinning to 300.
If you have skinning from the beginning, you shouldn't really concern yourself for the best location to farm leather. Every beast drops leather...
On the other hand, if you really want to make yourself nice and easy money, go to Duskwood, travel south of the Darkshire to the spot where there are those Vile Fangs and Tainted Ones (and other of their kind). These are the only monsters in the game that I know of that drop money (and cloth) and can also be skinned.