I have been doing Firelands Solo runs lately. If you kill all the trash within and the boss and loot absolutely everything, you can get up to 700g (if not more).
A single trash group drops up to 7 gold and bosses gives you ~25g each. I also had a lot of green/grey drops that sell for anything between 5g and 20g. Some of the epic drops might even be worth something still in the AH, worth a shot
With my ilevel 547 warrior I was able to clear the entire raid in roughly 30 minutes (and I took my time)
Depending on how many of your toons are level 90 and can solo this, you might have a good income. Other Cata raids might also be worth a shot, haven't checked those just yet, will do over the weekend
Just in general if you kill mobs. loot absolutely everything, even greys. small amounts if you take them to the vendor but it does add up nicely