I've been thinking.... man Wrath Of The Lich King was awesome... but it's coming to an end very quickly. I thought... what item is going to have a huge increase in price because it's farmed for in Wrath Of The Lich King and won't be farmed as heavily in Cataclysm? I instantly thought, the Argent Tournament Pets! These things will rise so much in value, because quite frankly, no one is going to farm these puppies come cataclysm!
So What's The Deal?
The Deal is that these things take ages to farm, even with doing everything, they are such a pain in the butt, I'm not even sure why they go for so low. Anyways, like I said right now they are a pain to farm, so I suggest stocking up on these pets before cataclysm hits as you won't see many around. Their prices are going to rice, regardless, Not many people are going to go out of their way to farm these pets, so it's best to pick them up before hand.
How much do I buy then for?
I've started buying them for as low as 350g per pet. You might think WOW that's extremely low! They currently AH for about 600-700g, but people are so desperate to get rid of these pets, you'd be amazed how many bites you'd get if you spammed trade for 30 minutes.
I've also started trading the pets cross faction as they have a even higher markup value. I can easily push for 1500g per pet if they are of the opposite faction.