Its actually harder than you think to find the best place to farm herbs. I have found a couple for you listed below. Now some of these herbs are going for more than 100g per stack, and you can get a stack worth in about 10 minutes if you just follow these maps.

Wild Steelbloom – Northern STV or Northern Stranglethorn

This is has by far the highest concentration of Wild Steelbloom with 91 notes listed here, the following also have some nodes but slightly less concentration of herbs. Stonetalon Mountains (84), Ashenvale (78), Arathi Highlands (64), Desolace (43),Wetlands (27), Duskwood (19), The Hinterlands (18),

Highest Concentration of Goldthorn – Arathi Highlands

65 Nodes of Golthorn are located here, other places this can be found are

, Dustwallow Marsh (48), The Hinterlands (45), Feralas (26), The Cape of Stranglethorn (19) and Desolace (11).

Sungrass in Eastern Plaguelands

Has over 250 Nodes here! you should be able to farm this stuff witin a few minutes per stack easy. Esp if you have a epic flyer . Other locations for this are

Thousand Needles (201), Badlands (84), Burning Steppes (75), Tanaris (46), Searing Gorge (37), Silithus (34), Un’Goro Crater (28

Khadgar’s Whisker in Eastern Plaguelands

Tons of nodes here over 350! other locations for Khadgars Whisker are

 Western Plaguelands (152), Feralas (132), The Cape of Stranglethorn (77), Arathi Highlands (50), Dustwallow Marsh (50), Desolace (40),