Herbs names and skill requirements
Peacebloom: 1
Silverleaf: 1
Earthroot: 15
Mageroyal: 50
Briarthorn: 70
Stranglekelp: 85
Bruiseweed: 100
Wild STeelbloom: 115
Grave Moss: 120
Kingsblood: 125
Liferoot: 150
Fadeleaf: 160
Goldthorn: 170
Khadgar's Whisker: 185
Wintersbite: 195
Firebloom: 205
Purple Lotus: 210
Arthas' Tears: 220
Sungrass: 230
Blindweed: 235
Ghost Mushroom: 245
Gromsblood: 250
Golden Sansam: 260
Dreamfoil: 270
Mountain Silversage: 280
Plaguebloom: 285
Icecap: 290
Black Lotus: 300
You can also use this nice chart, to find the lvl requirements and the locations:
http://www.worldofwar.net/professions/herbalism/herblist.php