4.2 comes Sell alot of your stockpile mats. Leather, volatile water/fire, enchants/gems/item enhancements, etc. for some spending cash, get around 100k the first day.
Http://www.wowhead.com/item=69237/living-ember
Living Ember
This is going to be THE key money maker in 4.2
One can only speculate where they will drop from. Since they are only adding dailies and raids. My guess would be from normal level raids and valor points. The average joe schmo could probably earn atleast 1-2 per week.
If you are a caster dps, you are going to be stockpiling these. Because they will be used for part of the legendary Staff chain (needs x25 living embers.)
The first 5 weeks or so they will probably cost 20-50k+ so if you can snag any for 5-15 you know you'll make some big money.
5 weeks later (estimate, time can change live version) the new daily profession rewards will come out and demand will shoot up more. Recipes for the epic boes will use about 4 living embers.
If you are a caster dps this legendary staff will probably be BiS for the rest of the expansion not to mention big bragging rights. This boils down to going for gold cap first or trying to make the staff. If you can make it go for it. But it's easily going to cost 500k+ gold to make.