1.Be a tank or healing class that can unlock the Call-To-Arms "CTA" satchel:
Satchel of Exotic Mysteries - Item - World of Warcraft
2.Run a heroic when CTA is for your spec (Call to Arms! Healers, Call to Arms! Tanks)
Make sure to run it alone. Don't group up with friends or guildies or you won't get a satchel.
3.Finish the instance, get your satchel!
4.Check your satchel (don't auto loot!) To see if theres anything inside you wish to keep on that character (for example a BoP mount) BUT DONT LOOT THE GOLD.
5.Send your satchel (since it's Bind to Account) to your Horde/Alliance alt.
6.Log onto your alt, check your mail, grab the satchel! Open it up, viola! You just traded yourself gold without a neutral auction house! (And maybe a pet, flask, or gem, too. Which you can then sell for more money.)
This may seem like common sense to some people, but many people were surprised this was doable when I told them about it.
Good luck =)