Well, I'm already rich enough from this so I guess it's time to share
Well, it's a known fact that the Argent Tournament pets are not BoP, and they can (and, for this matter, they must) be traded.
I got 2 ways of making a great deal of money by selling such pets, but for both ways, you'll need some gold to invest:
1- Selling your own faction pets on the Neutral Auction House:
You need at least 1000g for this one, or you must be willing to give up on 40 champions seals to buy a pet, and try to sell it on the neutral auction house. Depending on the server and the people that plays on it, you can resell it for up to 2000-5000g on the neutral AH
[edit] You must go after the pets for 1000g on the trade channel or icecrown's general chat (that's what I've been doing). A lot of people don't care about the seals and are definitely willing to sell the pets for 1000g.
Profit: 1000-4000g/pet
2- Selling opposite faction pets on your faction's AH. This needs a lot more of money invested - you will need to buy the opposite faction pets on the Neutral AH, those, like I said, will be on the margin of 2000-5000g. The point in buying those in the neutral AH to put on the factions is that no many people go to neutral AH's to buy stuff. You can put on your own faction AH for like 5000g-10000g, depending on how much you paid for it in first place.
Profit: 3000-5000g/pet
I already made around 30k with this in only 2 days, I'd try to do as early as you can, or maybe the collectors on your server will get hold of the pets before you could sell them.
Good luck and good selling =)