Outside of Tailoring & Enchanting (previous post), Inscription is currently the best profession for making gold. However, it can be rather time consuming because there are so many people competing on the Auction House, and you have to monitor your sales every 30 minutes to ensure that no one is undercutting you.
If you're okay with that, investing 2-10G of mats and getting a return of 20-100G per Inscription is a very lucrative method. Especially with Cataclysm coming out soon, you can make a killing on low-to-mid level inscriptions.
The other method which I use quite often is Cross Faction AH Trading (2 accounts are required for this, so get a friend to help you out and you can split the profits.)
There are plenty of guides to trading Gems/Ores/Epic Recipes from one PVP faction to another, however all of the servers I am on have identical pricing on each others' Auction Houses. So, those Gold Making tricks have never worked for me.
However, what DOES work (and very well) are selling faction-exclusive recipes and pets.
1. [Recipe: Kaldorei Spider Kabob]
Create a new Night Elf toon (no leveling required), run to Dolanaar, and mail yourself 7 Small Spider Legs and 2 silver. Go to the Cooking trainer there, learn first recipe, then a quest appears. Accept it, turn in the Spider Legs for the recipe. This toon can then be deleted (and a new one created) once you mail the recipe to your primary character.
Transfer it through the Neutral AH to the Horde side and put on the Horde Auction House for 300-500G. This recipe also sells on the Alliance AH for 100-200G.
Most NE toons just learn this recipe when they first start out and forget all about it. It's hardly ever on the AH, and folks need the extremely rare recipe for their achievements.. they usually have gold to burn too. I buy out Spider Legs on both Auction Houses so that I can quickly mail the cooking quest requirements to each toon I create too.
2. [Recipe: Roasted Moongraze Tenderloin]
Same approach as above. Create a new Draenei toon, level to 6, get "The Great Moongraze Hunt" quest from the hunter trainer at Azure Watch. Transfer through Neutral AH, sell on Horde AH for 300-500G. You might be able to get away with 1000G each, since it's even more rare than the Night Elf recipe.
3. Unlimited Supply Faction-Specific Cooking Recipes
Buy for pennies, sell on the opposite faction AH for 15-30G each. I typically sell 3-5 of EACH on a daily basis.
I usually just focus on the recipes sold by Kendor, because I can buy 12 or 24 at a time, mail them to my counterpart in Booty Bay to transfer through the Neutral AH. However, there are a ton of other "rare" faction-exclusive items below that you can also sell on the Neutral AH (have to sell much cheaper) or on the opposite faction side.
PURCHASE ON ALLIANCE SIDE:
[Recipe: Beer Basted Boar Ribs] - Sold by Kendor Kabonka
[Recipe: Blood Sausage] - Sold by Kendor Kabonka
[Recipe: Murloc Fin Soup] - Sold by Kendor Kabonka
[Recipe: Redridge Goulash] - Sold by Kendor Kabonka
[Recipe: Westfall Stew] - Sold by Kendor Kabonka
[Recipe: Seasoned Wolf Kabob] - Sold by Kendor Kabonka
[Recipe: Crocolisk Gumbo] - Sold by Kendor Kabonka
[Recipe: Crocolisk Steak] - Sold by Kendor Kabonka
[Recipe: Gooey Spider Cake] - Sold by Kendor Kabonka
[Recipe: Goretusk Liver Pie] - Sold by Kendor Kabonka
[Recipe: Fillet of Frenzy] - Sold by Laird
[Recipe: Loch Frenzy Delight] - Sold by Khara Deepwater
[Recipe: Clam Chowder] - Sold by Kriggon Talsone & Heldan Galesong
[Schematic: Blue Firework] - Sold by Gearcutter Cogspinner & Darian Singh (Sells for 25-40G each on Horde AH)
[Pattern: Black Whelp Cloak] - Sold by Clyde Ranthal
[Pattern: Black Whelp Tunic] - Sold by Amy Davenport
[Pattern: Herbalist's Gloves] - Sold by Harlown Darkweave
[Pattern: Raptor Hide Belt] - Sold by Androd Fadran
[Pattern: Red Whelp Gloves] - Sold by Wenna Silkbeard
[Pattern: Bright Yellow Shirt] - Sold by Danielle Zipstitch
PURCHASE ON HORDE SIDE:
[Recipe: Bat Bites] - Sold by Master Chef Mouldier
[Recipe: Crispy Bat Wing] - Sold by Abigail Shiel
[Recipe: Crispy Lizard Tail] - Sold by Tari'qa
[Recipe: Heavy Crocolisk Stew] - Sold by Ogg'marr
[Recipe: Lynx Steak] - Sold by Landraelanis
[Recipe: Roasted Kodo Meat] - Sold by Wunna Darkmane
[Recipe: Scorpid Surprise] - Sold by Grimtak
[Formula: Enchant Chest - Lesser Mana] - Sold by Kithas (Sells for 40G each on Alliance AH)
[Schematic: Red Firework] - Sold by Sovik (Sells for 25-40G each on Alliance AH)
[Pattern: Raptor Hide Harness] - Sold by Tunkk
4. Same approach as #3 but for Faction Exclusive Pets.
Snakes in Orgimmar (e.g. [Black Kingsnake]), for example, sell for 40-50G each on the Alliance side, and you can purchase an unlimited number of these. I sell 2-3 of each daily.
HORDE
[Crimson Snake] – Xan'tish, Orgrimmar
[Brown Snake] – Xan'tish, Orgrimmar
[Black Kingsnake] – Xan'tish, Orgrimmar
[Brown Prairie Dog] – Halpa, Thunderbluff
[Cockroach] – Jeremiah Payson, Undercity
[Golden Dragonhawk Hatchling] – Jilanne, Fairbreeze Village
[Red Dragonhawk Hatchling] – Jilanne, Fairbreeze Village
[Silver Dragonhawk Hatchling] – Jilanne, Fairbreeze Village
[Black Tabby] - Drops only from Alliance-friendly NPCs.
ALLIANCE
[Bombay] – Donni Anthania, Elwynn Forest
[Cornish Rex] – Donni Anthania, Elwynn Forest
[Orange Tabby] – Donni Anthania, Elwynn Forest
[Silver Tabby] – Donni Anthania, Elwynn Forest
[White Kitten] – Lil Timmy, Stormwind
[Snowshoe Rabbit] – Yarlyn Amberstill
[Great Horned Owl] – Shylenai, Darnassus
[Hawk Owl] – Shylenai, Darnassus
[Blue Moth] – Sixx, The Exodar
[White Moth] – Sixx, The Exodar
[Yellow Moth] – Sixx, The Exodar
There are also Parrots in Booty Bay, some people are too lazy to travel there to buy them or don't even know where they are sold. And the Argent Tournament pets sell for 1000-2000G each, but they require work and time to collect the required points to purchase.
5. [Recipe: Savory Deviate Delight]
My other favorite. I buy these on the Horde AH for 10-100G each, then sell on the Alliance AH for 900G. I can sell 1 or 2 daily easy.
6. Faction-exclusive even-more-rare recipes/plans. Time consuming, but high reward.
Create a new Deathknight character, run through the intro quests, and then level up their professions (options below) as quickly and cheaply as they can. Do the quest, get the reward (non-BOP recipe), and sell on the opposing faction's AH for big money. They will take a longer time to sell (because no one is ever looking for them), but you can sell for 2000-5000G because of their rareness. (Trade Chat announcements help.)
ALLIANCE SIDE:
[Plans: Golden Scale Gauntlets] - "The Origins of Smithing" (Req: Level 40, 205 BS)
[Plans: Heavy Copper Longsword] - "Supplying the Front" (Req: Level 12, 35 BS)
[Plans: Ironforge Breastplate] - "Gearing Redridge" (Req: Level 16, 100 BS)
[Recipe: Tasty Lion Steak] - "Costly Menace" (Req: Level 34, 150 Cooking)
[Pattern: Moonglow Vest] - "Moonglow Vest" (Req: Level 18, 90 Leatherworking)
HORDE SIDE:
[Recipe: Discolored Healing Potion] - "Wild Hearts" (Req: Level 11)
[Plans: Barbaric Iron Boots] - "Trampled Under Foot" (Req: Level 36, BS 140)
[Plans: Barbaric Iron Breastplate] - "Barbaric Battlements" (Req: Level 32, BS 140)
[Plans: Barbaric Iron Gloves] - "Joys of Omosh" (Req: Level 36, BS 140)
[Plans: Barbaric Iron Helm] - "Horns of Frenzy" (Req: Level 36, BS 140)
[Plans: Barbaric Iron Shoulders] - "On Iron Pauldrons" (Req: Level 32, BS 140)
[Pattern: Kodo Hide Bag] - "Kodo Hide Bag" (Req: Level 10, LW 10)
If you have no need for the recipes/plans, you could just use existing characters if they are high enough level.
As you can see, there are a ton of ways to do this. Use Auctioneer to determine which recipes are least available on the AH to find the most valuable and rare if you want. I just do a fraction of the amount listed above, but I can still pull in 3000G per day easily (1-2 hours work max, no boring grinding.)
I have no idea why gold farmers spend all of their time grinding when 10x the amount of gold can be made using the strategies I have posted. =]
