Azshara's Veil and Stormvine are the two herbs found in Vashj'ir, Azshara's Veil being (almost) unique to the zone.
The herbs can be found through all three sub-zones, Kelp'thar Forest, Shimmering Expanse, and Abyssal Depths and mainly occur on the sea floor, though occasionally you will find them on elevated mega-plants, structures or ledges. The red line on the diagram shows the optimal Azshara's Veil and Stormvine herbalism route. Notice that it only winds through Shimmering Expanse and Abyssal Depths. While Kelp'thar Forest does contain herb nodes, it seems that there is a higher concentration of them in the final two zones of the undersea world. Also of special note to those who have both Mining and Herbalism as their professions, the optimal Obsidium Ore route in Vashj'ir is also represented by the red line in the diagram and coincides almost exactly with the optimal herbing route.
Vashj'ir is a special opportunity for raw material farming because there are certain barriers of entry that prevent players from just diving straight in and farming. If you don't have seal form as a druid, it is necessary to obtain a Subdued Abyssal Seahorse mount for greatly increased swim speed. You'll need to complete the first half-dozen (or thereabouts) quests in the zone until you get to the seahorse quest.
The other opportunity in Vashj'ir is that it provides a unique herb that may retain its value at the auction house much longer than other herbs in the Cataclysm expansion because of it being a low 80's zone and because many players shy away from gimmicky zones that require something like a seahorse to get around in. Many players will skip it all together in favor of Mount Hyjal and Deepholm, which means more opportunity for the savvy farmer to make more WoW gold per hour spent farming.
Mount Hyjal Mining Route
Vashj'ir Mining Route
Deepholm Mining Route
Uldum Mining Route
Twilight Highlands Mining Route
Mount Hyjal Herbalism Route
Vashj'ir Azshara's Veil and Stormvine Route
Deepholm Heartblossom Route
Uldum Whiptail Route
Twilight Highlands Twilight Jasmine Route
Tol Barad Azshara's Veil and Whiptail Herbalism Route