Crafting with inscription requires the inscriber to get pigments from herbs. The process, called milling, is similar to jewelcrafting's prospecting: five herbs are destroyed to create a small quantity (1-3) of pigments. A few beta testers have put out levelling guides describing how to powerlevel the skill, but those guides have shied away from recommending specific herbs to mill. That makes sense: herb prices vary from server to server, and since the craft is still deep in the playtesting process, there's a good chance that any recommendations made now will be obsolete when it goes live.
However, since many of us here are already stockpiling herbs to powerlevel or profit when the craft goes live, I'm going to share my thoughts on what herbs to procure. Different pigments come from different tiers of inks; you get the same pigment from milling peacebloom as you do from silverleaf, bloodthistle, earthroot and mageroyal. So there's no point in milling earthroot, which is generally the most expensive of these herbs, instead of bloodthistle or peacebloom, which are generally the cheapest. Of course, none of these early herbs cost more than a handful of silver anyway, so bargain hunting isn't very rewarding at this level. To powerlevel, I suggest buying a stack of peacebloom and a stack of silverleaf (these herbs are used straight in an early ink), and three stacks of any of these herbs. I wouldn't bother stockpiling these low-value herbs.
The next pigment comes from briarthorn, bruiseweed, stranglekelp and swiftthistle. Bruiseweed is generally the cheapest of these. Get two stacks of it for powerleveling. Stockpiling it doesn't seem like it would be very profitable, since so little of this ink is needed for powerlevelling.
The next hit on the pigment parade is from kingsblood, gravemoss, liferoot or wild steelbloom. Kingsblood and liferoot are generally cheaper than the other two. You'll want five stacks total of the two of them combined for powerlevelling. Stockpiling these herbs might be quite profitable--they're cheap enough that you could mark them up pretty heavily and still have a stack cost less than someone gets from a single daily quest. People unfamiliar with the herb market won't balk at that price, leaving you a huge profit margin.
The next pigment is found in goldthorn, fadeleaf, khadgar's whisker, and wintersbite. Anyone who has ever leveled herbalism knows just how common and how hard to sell khadgar's whisker is. Powerlevel with 5 stacks of that cheap herb, and stockpile it for more huge profits come inscription.
There's many sources for the next pigment: blindweed, sungrass, firebloom, purple lotus, arthas' tears, ghost mushroom and gromsblood. Here server prices begin to vary wildly: purple lotus is cheapest on one server I know, arthas' tears on another, and blindweed on another, with enormous price differences differentiating them. Still, any of the above are likely to be cheaper than sungrass, much less ghost mushroom or gromsblood. You'll need a whopping twelve stacks for powerlevelling. If you have the budget to stage a buyout of these herbs, you might be able to corner the market. That's a risky move, but could pay big. Stockpiling is bound to be profitable, as these herbs are spread out and not terribly easy to farm.
They're easier to farm than the next tier of herbs, though: golden sansam, dreamfoil, mountain silversage, plaguebloom and icecap. Expect to pay a gold or more each for all these herbs. Icecap might be the exception--the demand for it has been so low, any on your AH might be quite cheap. Otherwise, you'll have to pay the high costs of golden sansam and dreamfoil, which tend to be cheaper than plaguebloom and silversage. You'll need 15 stacks for powerlevelling. These are the herbs to farm in anticipation of inscription--they're hugely profitable now, and their value will only go up. Their high prices make stockpiling from the AH or trying to corner the market expensive, but the potential profit is huge.
The last pigment available before the expansion comes from Outland herbs: dreaming glory, felweed, flame cap, mana thistle, netherbloom, nightmare vine, ragveil, teracone and ancient lichen. The volume of these herbs should be quite high on your AH, but steady demand keeps the price up in many cases. I've found that felweed goes up at low prices, however, sometimes cheaper than khadgar's whisker. Buy plenty of it; you'll need 15 stacks or so for power leveling. At those prices, buying some to mark up on inscription day might also pay off well--again, there are people who don't know the market.
These herbs will get you the pigments to make the inks to craft the glyphs that will level a character to 350 inscription, or even to 375 though waiting until the expansion for those 25 points would be economical--the next pigment comes from Northrend herbs only, and makes an ink that is yellow at 350 inscription.
Good luck to you all. May flowers turn to gold in your pockets.