First, let me say I'm not an advocate for grinding, nor questing for gold. However, some people enjoy it. I like to optimize my time, whether I'm playing WoW, working or in the gym, and I just don't feel that it's a good use of time for me. To each their own, however, and I know people do it. Let's look at why:
1.) Instant gratification. You either get 13g/16g instantly plus a quest reward turning in quests, plus trash and silver drops.
2.) Materials and Uncommon items. Unless you're fighting mobs that don't drop loot, you'll more than likely come across massive amounts of cloth and Uncommon items to either Disenchant or sell as-is on the Auction House.
3.) Possibility to come across nodes. If you're a skinner, you may be able to skin the quest mobs/mobs you're grinding on. If you're a miner/herbalist, you could maybe find herbs or mineral nodes to harvest while you're questing or grinding. More profit.
This is all sounding good so far. Let's look at it a little deeper.
If you quested until 85, and did all the quests in all the zones (or at least most of them), without any instances or experience bonuses (heirloom pieces, guild perk, etc.), you probably hit 85 somewhere in the Twilight Highlands, assuming you started in Vashj'ir or Mount Hyjal (and didn't do the other starting zone). That's a lot of parentheses. Anyway, this leaves very little to do in the way of quests to make gold, however, you can do dailies! Hooray!
Wildhammer/Dragonmaw Clan has dailies in Twilight Highlands, Therazene has dailies in Deepholm, and Ramhaken has a couple quests. You won't get a ton of gold, but you'll get a little bit and faction rep (which is why people do these dailies anyway). So where's the money? Doing old quests.
WHAT but why would I do those, rewards are outdated and bluh bluh whatever. Let's be cereal for a minute here. Old quests (green quests) are easier to complete. Mobs have 13,000 hp as opposed to 70,000hp, and there's nobody there. So, what do? Go kill those guys. You'll be surprised to see that the silver drops aren't that much lower, but 1.) Nobody will be farming them, and 2.) You'll kill them a lot quicker. Not to mention, the rewards for each of the Ramhaken daily quests (aside from the reputation) is 10g. The reward from the Icecrown tournament dailies is 13g. Which wins? Yeah, I thought so.
In addition, there are 2 great spots in Icecrown to grind gold. See image:
The yellow part is where you should go for AoE farming: There are a lot of Converted Heroes here, for the daily and also for your grinding pleasure. Each one will drop roughly 20s, and they come in packs of 5-6. Mix that in with the grey items that vendor for around 1g each (on average), the cloth and greens, and you have yourself a nice little farming spot.
The red part is where you go for huge single-target damage. The Hidden Hollow, below Onslaught Harbor, houses elite level 80 mobs, who have in the vicinity of 20,000hp. Should be cake at level 85. They drop about a gold each, around 6 frostweave, and of course the usual assortment of Uncommon and vendor trash items. Onslaught Darkweaver is one, and I've forgotten the name of the melee mob that resides here as well. A half hour in the cave should net you at least 300g, if not more.