So, in my speculation about stock-piling and what's coming up, I've thought of a few general things to consider in general when considering stock-piles.
Is there anything better that will replace end product in Cataclysm? A great example of this is weapon enchants. I heard someone in guild chat mention stocking up on mats for Mongoose because it was the best enchant. This is a terrible mistake, and obvious this person didn't look anything up. There's quite a few very good (while bland) enchantments coming out in Cataclysm.
Will people need this to level a profession? Is it a popular material in leveling a profession? Can I provide enough of said material to make someone want to purchase my item to fill their leveling needs? Is it a bottle-neck material? There are some items out there, that will always sell because they are always needed for one or more professions, but are also abundant in the game. There are also items out there that leveling guides list to use, and recipes that need to be purchased from a vendor. There are also items that are not easily found, but some people will buy them up (this is higher risk) if there's enough to level a profession if the end product is worth-while, or if there's a lack of other things, this works great in a bottle-neck. And then of course there's mats in bottle-necks. A good example of this is alchemy. In order to max out 450 alchemy, you need to transmute meta gems, so the materials for these are a worth-while investment. However, with Cataclysm coming out, it's always good to stay on top of whether these materials will still be desired for leveling, or bottle-necked.
What about achievements? There are many achievements that require consumption of items, wearing items while dancing under the influence, or reputation hand-ins as we saw with Insane in the Membrane, or Sporeggar. These are often items worth adding to a snatch list to be purchased at a low-price and flip for extremely easy gold. Let's not forget the upcoming guild achievements that may use a substantial amount of consumable items.
I've been looking at a few items lately, especially Saronite Ore, to keep a tidy little stock-pile of for Cataclysm. Eternals are another item I think is worth stock-piling, especially Life, Water and Fire. Shadow is a bit more common from mining, but worth holding on to. Making money off these items is all about supply and demand however, so you need to be sure you know your server's markets.
Saronite Ore can be sold raw, in bars, transmuted to Titanium bars and further made into Titansteel which is used in mounts that will still be sought-after in Cataclysm. It can also be prospected and turned into gems that Jewelcrafters need to level, and Alchemists need to x-mute for levels. Yellow epic gems are used to make the engineering Jeeves which may be desired.
Eternals are used in everything to level, especially the 4 I listed. Earth isn't used as much, but can be used to create infinite dust in Cata if there is a demand for it on your server as well. Frozen orbs are also needed for a few items, and can easily be traded for Eternals. I'd keep my eye out in Cata to use Frozen Orbs as a flipping item.
Any ways, just my thoughts, probably not the most original things, but a good process to get your brain thinking.