To preface, this is all speculation, and pretty uneducated speculation at that, as I am no expert by any means, so I encourage you to think about this yourself, and perhaps prove me wrong if need be. So, that said, here are some market predictions!
Pink Turnip: Remember when I pointed out that my guild is going to need A LOT of these things every week? Well, this is going to be the case with every guild who decides to use the main feast for raiding. As I doubt many of them will have the foresight or coordination to produce these in-guild, at least in the first few months of the expansion, I expect this vegetable to become relatively scarce and high-priced during that period. Don't expect to be selling many until about a week or two into the expansion though, as it takes a week for the first raid to open up, and it also takes a lot of cooking(and thus, a lot of other materials) to get to the point where you can even buy the recipe for the feast. Here, to illustrate what I think will happen, a highly scientific analysis made with Paint:
The Jogu Flip: There is a little drunk NPC in Halfhill(the main city in Valley of the Four Winds), who, for a fee(free if you raise his reputation to exalted) will let you in on what crops are good to grow that day, meaning that you will get more from those crops. Now, there are two ways to go about using this information. The first and most obvious is to plant what he says is good to plant, and thus have more to sell on the AH, or to turn into Bags of Groceries for tokens. The second way is to take advantage of people who use the first way, and buy the crops that they post the day of/after heeding Jogu's advice. I predict that the price for these crops will be temporarily lower due to the increased supply on the AH, but will quickly return to normal, because most crops are used a lot in cooking recipes(meaning, that there will be a lot of movement in this market). If you are observant, you can take advantage of this temporary fluctuation in the price, and flip the crops after they go back up to non-inflated prices. Now, this depends on if the profit you can gain will be more than the price for listing the crops, or will be enough to even make it worth the time. I think it will be, at least in the first few months at least, as I think cooking materials will be very high priced during that time.
Archaeology Keystones: The Lorewalkers are likely to be a very popular faction in Mists. Not only do they give a sweet-looking mount at exalted, but they also are the faction one has to grind(to revered, so not too bad) to get belt buckles. Thing is, I really doubt that many people have taken the time to get their archaeology up during Cataclysm. This may just be my perception, but it just didn't seem too popular, especially with the non-casual crowd. Well, when they find out that the best way to grind reputation with the Lorewalkers is to have archaeology(and specifically on their Blacksmith), there will be a lot of people going out and grinding it. This means, obviously, many more keystones(the items used to help complete certain relics) being in demand. Of course, the increased number of people grinding out archaeology may bring more keystones into the market, but I doubt it will be enough to cover the amount in demand. I have ground the profession to 525 myself, and I can attest to not getting enough keystones from just my grinding. If they are cheap on the AH now, pick some up and hold them until the start of the next xpac.
Anyway, that is it for now, hope these three markets end up panning out, and working for some of you! Let me know what you think!