One of the most profitable market to dabble in has always been the twinking market. The reason behind this is fairly simple, it is a market that is selling the best possible items for a given level to a character that simply wants to be the best in PvP at that given bracket. Well for the duration of the last two expansions i have been silently racking up quite a bit of profit from selling a given item, and today i am spilling the beans.
I won't get into making this a very long post as unlike the usual topic that i like to cover in my posts, today i will cover just a given item. This item that i am talking about is Hard Khorium Band and as you can see it is a ring that just happens to be BiS for Agi users.
The reason why this is a very good market is that if you are able to craft the given item you can monopolize on it as it is a niche market that very few to none suppliers are looking at. There is a tricky part to this though, in order for one to be able to craft this item you would need to obtain two patterns, the first one is for the actual Hard Khorium Band and the second one would require a miner so you would be able to Smelt Hardened Khorium.
Now you know how to make the item and how to smelt the given materials, so the next step in selling the item would be to define the means on how to sell the item. There are two ways you can go about this, the first one is to put it up on the AH and wait for people that know what they are looking for to buy it, and the second way is to actively advertise it as a BiS item. The second way has a much higher selling chance but at the same time you will be opening up your niche market to the competition. I will leave it up to you to decide the course you want to take, but if you are going for the second option make sure that in your barking advertisement macro you put the spotlight on the fact that the ring is BiS for Twinks, and that if they want to be the best they need to get it. ( Just make sure your macro is catchy, informative and borderline cheesy )
And last but not least, if no one is holding this market you will have the chance to set the price to your liking. The going price for this item has been moving from 1k in TBC, then 3-5k in WOTLK and nowadays it can be sold for up to 10k as people don't mind paying the price if you can make them think that they are paying for THE BEST item they can get for their character.
So to sum it up before i finish up, you will need a character that has Jewelcrafting and Mining (ideally), you will need to have the two patterns that both drop in Sunwell and you need to know that you will be marketing your item to Rogues, Shamans and Hunters that are twinking in the 70's PvP bracket. So by knowing all this and hopefully having these patterns you can make a decent profit if you decide to hold that market.
So, like always, keep an eye out for good opportunities out there.