So some people may or may not be doing this already, but ive found a way on my server to make a pretty hefty ton of cash.

Run a opposite faction bank alt, to the shared AH so you can trade ect with yourself. (make sure to get fp's).
I started selling just one argent pet from horde side, to the alliance. This was going for about 600g my side, to 1200g their side. I have since sold numerous pets and for a while have been just bouncing them back and forth.

--- Cute things sell! To many women around imo. Sell lambs, mechano peeps, mulgore hatchlings, broomsticks and stuff all have netted me good money. I have been selling for 1k bid, 1200 b/o sometimes +/- 100g on both with much success. Same goes for certain things you can look at, check alliance for enchanting mats or eternals or green gems can get good deals going both ways. Multiboxers are at an advantage since we can trade with ourselves using different accounts. Just watch trying to pass large amounts of gold through blackwater since their taxes are so high.

So in closing if you have not done this yet, look at selling pets between factions. So far ive netted about 10k gold doing this in just profit.