Portals and Potions
With the removal of portals from both Shattrath and Dalaran, mages are still making easy gold off of players that still were parked in either of those cities. People are returning to the game and are paying upwards of 30g for a portal out to main cities. Others are simply logging in an alt for the first time only to discover them trapped within Dalaran and looking for a quick way out. Portals aren't the only travel mode these days. Scribes have their option, but alchemists now have a way to profit off of other player's travel.
Another common question I've been seeing in trade chat is "How do I get back to Deepholm?" Anytime I see this asked, I reply back with, "Use a Potion of Deepholm!" This most always results in an instant sale on the auction house for the alchemist dabbling in that market. The reply is usually followed with a "Thanks, I just got one!"
Potion of Deepholm
This teleports the drinker to Deepholm. The potion of deepholm requires 5 Heartblossom and 1 crystal vial. The drinking player must be level 82, but you had to be level 82 to start the quest to allow entry into Deepholm anyway. The potion requires a skill level of 525 Alchemy to craft.
Mage Bubble Hearth
Some players use these potions to return to Deepholm, but others use them as an extra hearth because they return you near a portal to your capital city. These are also the only way to accomplish the new bubble-hearth trick, but only for mages! This potion isn't usable in combat so a mage can cast Invisibility and drink this instant cast potion while invisible. It's the new mage bubble hearth so sales may be higher on Warcraft PvP servers.