Blacksmith probably has one of the good ways of making gold where you can craft items that are in a constant demand due to the game's mechanics and player needs. Here i'll try and note out the best ways that you can use your blacksmith to make gold, oh and if you've missed the previous post about the enchanting rods check it out.
Ok to get down to business i'll try and make it easy and fast to see what you should be focusing on.
Ebonsteel Belt Buckle
Pyrium Weapon Chain
These two items are always in high demands because EVERYONE uses the belt buckle and as for the weapon chain, hell all the PvPers love it for some reason so they sell quite well and take into account that it costs only 1 Pyrium Bar and it usually sells for 50-150g then you have to love it, every single sale.
Yes this is the WOTLK version of the Belt Buckle, and before you ask yourself why bother crafting those then check out the little bit of info that says you can't use it on item level above 300 but that only means that you can use it on lower level, and yes that means people that are leveling and most notably higher tier twinks.
One of the things you should check is the competition and the prices they are posting, i usually corner the market and post them for 200G, and usually during the late night shuffle.
This set is where you make alot of gold and you don't even have to check recheck and triple recheck for undercuts because it's usually one or two guys holding the markets and rechecking the prices every 6-12 hours, so with minimal effort you could be carpet bombing the profits on those pieces.
One of the main reasons why this set is so profitable is because it's aimed at all the people that are into PvP and are leveling an alt or just starting out in PvP and they buy that gear as a entry level gear to help them not die right away in BG's or Arena. And the best part about this set is it's aimed at Warriors, Paladins and Death Knights so it's pretty much covering 3 classes which is a pretty big market.
As for pricing i use a very wide pricing net which means 200 - 1250g and solely because usually people do silly things like posting 5 of each at ridiculous low prices but still profit like 130g or something but for some reason i don't like profiting 30-40g on an item that i sold for 1250g the night before, so my advice don't go below 200g
Bloodthirsty Ornate Pyrium PvP
Now this set is a bit more different from the previous one for one reason alone, it's meant for the holy paladins alone and in perspective it has a much more narrower crowd of buyers and in return the profits are lower.
And as a finisher i'd have to add that blacksmith has one of the best uses for the Chaos Orbs, which means that if you have done the dailies for the Molten Front and have access to the patterns for the BoE weapons you can earn tens of thousands of gold by simply crafting those weapons ... you dont even have to but the mats just offer your services and say you charge 5-6k for the orbs and you will get some people asking you to do it for them.