I'm in the same boat as you. Back when patch 4.3 came out, I had prepped well for it and made about 100k a day for about 2 weeks. With all that gold, I re-invested heavily in preparation for MoP.
I've been stockpiling since Nov 2011 by buying low cost mats for everything - from skinning to mining. I have 2 accounts and 14 toons total, each with maxed out guild banks and tabs full of mats ready to go. My plan is to initially sell glyphs and bags and pets. Then I will type /who monk on a daily basis to get an idea of when the monk alts may need certain mats and start selling goods on the AH.
For the last 2 weeks, I've been posting everything in small batches at 1000-2000% mark up to populate theunderminejournal and any AH add-ons with inflated prices to throw off my competition. In fact, I've barely sold anything at the inflated price but lately I've noticed my competitors are matching my prices. I've posted essences of air for 400g a pop and my competition are matching my prices. lol.
Now, I have to resist the urge to drop my prices too early. My plan is to sell a fraction of my items at hugely inflated prices for the first month, and then slowly lower prices to sell the rest of my stockpile as a hedge against inflation.
I've changed to dual gatherer on my Druid, and leveled Inscription on 10 chars (very easy to do while Cataclysm herbs are so cheap). Inscription will be THE best profession for making gold.
- DMF Decks are always a good seller, and there's enough time to get a few decks before November's DMF. The decks stay BiS for a couple of tiers.
- Shoulder enchants. The blue quality ones will sell quickly to players that have just dinged 90, then the epic ones for those starting to get raid gear/heroic gear.
- Off-hands and staves. The reagent they require has a cooldown, and you arn't guaranteed to proc it, but when you get 5 (off hands) or 20 (staves) expect to make a lot of gold.
- Glyphs. Loads of new glyphs to discover which means for the first week or so you will sell the decent ones extremely fast and for a lot of gold.
Best part is all it requires is herbs, lots and lots of herbs. You should get enough Spirit of Harmony from levelling, and then you also get them from gathering professions.