This is actually more of an addendum to "Part 2".
In Part 2, I had discussed how there are many items, pets, and recipes that are Faction Exclusive (can only be obtained by one faction), and how they can sell very well on the other side. I forgot to list one interesting item that you can transfer through the Neutral AH from the Horde side to Alliance that's highly valuable.
To Horde players, it's trash. But to the Alliance, it's pure gold. =]
I'm referring to the [Sleeveless T-Shirt]
What most players don't know is that the [Sleeveless T-Shirt] only drops from Alliance bodies in Alterac Valley, so it's impossible for Alliance players to obtain this item unless it's through the Neutral Auction House.
They're cool looking outfits and their description is priceless. You can actually sell them for 50-100G on the Alliance auction house. Or just throw them up onto the Neutral AH for a reduced price. =]
Right now, the gold markets seem to be favoring Glyphs and Recipes/Pets (cross-faction trading works very well), but disenchants aren't selling for very much anymore. But then again, it's server dependent.
Here are some other interesting items that can be sold Cross-Faction.
1. The [Black Tabby] pet can only be obtained by the Horde, killing the Dalaran Spellscribe in the Alliance-friendly village Ambermill. The silver elite spawns quite a bit at 3 different locations (Humanoid Tracking is recommended so that you can login/logout and just quickly scan the area for the Spellscribe) throughout the day, but the Pet drop rate is around 20%. It'll easily sell for 700-1000G on the Alliance AH.
What's nice about the other NPCs in Ambermill is that they drop other rate items that can only be obtained by Horde. Such as "Channeler's Staff", "Dalaran Wizard's Robe", and "Jewel-Encrusted Sash". Alliance don't really know how rare they are (and that the Robe is required to look like a Dalaran Wizard) so your best bet is to advertise in Alliance trade chat. I sell the Robes for 75G each, and the Sash/Staff for 20-30G a piece. Their drop rates are very high, which is nice.
2. [Ripped Ogre Loincloth]
This item can only be obtained by Horde when looting the Gordunni Dirt Mounds (Gordunni Cobalt quest in Feralas). They look awesome, very rare on Alliance side, and I sell for 75G each.
Old World items are also selling very well right now, but they won't be as soon as Cataclysm hits. On my server for example, here's how much they sell for:
Adamantite - 60G/stack
Fel Iron Bars - 70G/stack
Goldthorn - 80G/stack
Purple Lotus - 80G/stack
Gromsblood - 80G/stack
Rugged Leather - 50G/stack
Wool Cloth - 30G/stack
Botters are still foolishly collecting WOTLK ores (ie, Saronite) and have no idea how well Fel Iron and other Old World items are selling. I report bots all of the time in WOTLK zones, but never see any in Outlands surprisingly.
Anyhow, in preparation I had stockpiled all of these items during the WOTLK launch (and prior to) when everyone was running new DKs. I filled up several Guild Bank Tabs with these items, and just waited for 4-6 months to sell them. I had paid about 5-10G per stack for most of these items and resold them at significantly higher prices.
With Cataclysm approaching, though, I would recommend that you sell all Old World items that you have right now and then buy them out again when everyone is leveling their fresh toons (only to resell them again 4 months down the road.) If you have the guild/bank space that is. =]
Speaking of Old World items, don't worry too much about farming the [Swift Zulian Tiger] either if you just want the cool looking mount. Everyone is saying "The Swift Zulian Tiger is gone forever! Farm them now while you still can!". However, according to my trusted sources it will actually be back in Cataclysm but much easier to obtain (the "Insane" title will also be available in Cataclysm but easier to get as well) with the Zul'Gurub zone rebuild and new quests. (The mount will still be a drop, reward, or an exalted reputation purchase - it's not exactly clear yet.) The achievement won't be the same though, only those who got the "original" will have that special mount and achievement, but there will be a new mount with the same look and texture.