Farming Molten Core Again
All of the older raids are easily soloable by anyone high enough in levels. For Molten Core, even a level 70 can easily clear this place if you know your class. No tactics needed.
Molten Core offers the following pets that can be sold:
Their price depends on how many other people are selling them on your realm, and also if you level them up before selling, their value increases a LOT and someone will also buy it faster then. Leveling a pet to 25 is not fast though, unless you have a level 25 pet that can boost. If no one else is selling them, I recommend to put a price tag of 5000 gold for starters, even if it's a level 1 pet. Level 25 pets usually sell for at least triple of what a level 1 sells, sometimes even 20x more.
On larger realms you're rarely the only one selling a certain pet, so check the prices if they are worth farming before doing anything.
I will post the remaining raids at some point too. Collect all of these pets and you will get a special achievement and an additional, unique pet as a reward!
More ways to make WoW Gold in Molten Core
Molten Core offers lots of other loot besides pets. Perhaps the most valuable item you could come across here is Teebu's Blazing Longsword, (one of the most coveted transmog items) as vanilla raid mobs have the highest chance of dropping old world epics. See what other loot can be found here!
Blood of the Mountain farming:
http://www.kujaswowgoldguide.com/2011/07/blood-of-mountain-makes-you-rich.html
Treasures in Molten Core:
http://www.kujaswowgoldguide.com/2011/06/loot-hunters-looting-in-molten-core.html