1. All of the Vanilla raids in-game (Naxx is treated as Vanilla for these purposes) can drop 3 different battle pets. Depending on the pet and server, they vary in price for ~200g to ~3000g. They can also be sold cross-server since pets are now account bound rather than server bound.
2. If you have a reliable way of resetting the trash after Broodlord in BWL, you can farm those mobs for things such as Teebu's Blazing Longsword.
3. BC raids are great sources of Netherweave cloth if you're willing to turn them into bags. Prices on them vary from 25g-50g per bag and have high turnover.
4. Sunwell is a source of some of the rarest crafting patterns in game but the prices on them aren't as good as they used to be.
5. WotLK raids are good sources of Frostweave though whether to sell them as cloth or bags is dependent on the server.
before they changed the way gold is dropping, there was a decent gold benefit during cata, my weekly income just from farming, BT, SSC, the eye, etc looting everything and sell it was about 7k gold, because each boss dropped about 250g but now a days i really dont know how much you can earn from clearing those old raids, maybe about the half maybe less, mostly i earn my gold from Auctions now