As you have seen if you read my post "What should I do?", I'm trying to get rid of a great amount of [Obsidium Ore] and related uncommon gems...
My server (or at least my faction on my server), as a great number of gold-farmers selling [Obsidium Ore] at less than what I call the Magic price for Obsidium Ore... i.e. the amount of gold you would make cutting the uncommon gems and selling them at the vendor (you usually make more gold than that just putting them raw on the AH).
I actually buy only when the price of [Obsidium Ore] is less than 40g a stack, and I still have too much Ores to sell everything I can make from them.
Well, something I found is going very well is selling [Obsidium Bar].
I'm actually putting them at 185g a stack and they actually sell very well... This seemed a bit strange to me, but I've been doing this for nearly a week without a great deal of competition. I checked the horde-side of my server, where there are less farmers, and there the prices for [Obsidium Bar] are a lot closer to what you need to make them.
I suppose that [Obsidium Bar] are selling well on my side of the server thanks to the gold-farmers: lots of players get tired of mining, since the competition was too hard for them... And they just forgot totally about that profession (or learned another one in its place) and so they're not smelting [Obsidium Bar].
This makes this knowledge very server-related, I know... But if your server is full of gold-farmers you should want to check if miners have stopped smelting [Obsidium Bar] (and maybe also [Elementium Bar] and[Hardened Elementium Bar]... Some time ago I made a post about selling Hardened Elementium Bars). I sell at least 10-15 stacks every day. Each one costs me less than 80g, and I price them all at 185g (even if there are some at less than that price... Usually there are so few [Obsidium Bar] that people start to buy mine in a brief time... Also because I'm the only one selling stacks and not singles).
What I like more in all of this is that... Well, smelting takes a lot less effort and thinking than prospecting! I just put my miner near a forge and go to do something else. When I come back I don't have 12 different kind items which I should sometime cut, sometime sell raw, sometime cut and vendor. I just have a good number of stacks of something I can immediately put in the AH! This cannot be done in all servers, but it's great if you can.