This Nightmare Vine farming guide will show you the routes that I use for farming Nightmare Vine. There were no major changes to herbs at Outland, so this guide can be used for Burning Crusade Classic (TBC) and Retail WoW.
Nightmare Vine usually grows out in the open as well as tucked in between rocks.
Shadowmoon Valley basically the only place where you can farm this herb effectively. You can also find some Nightmare Vine in Blade's Edge Mountains, but only 2-3 nodes.
Blade's Edge Mountains
You will only get a few Nightmare Vine here, but overall a great farming route. You will get a lot of Dreaming Glory, Felweed, and some Mana Thistle.