Well, there are

-Great Stamina: 3/3 for 4/8/12% increase in pet stamina
-Natural Armor: 2/2 for 5/10% increase in pet armor
-Blood of the Rhino: 2/2 for 1/2% increase in pet Stamina and 20/40% increased healing taken by the pet (also requires 3 points in Greater Stamina)
-Pet Barding 2/2 for 3/6% increase in pet armor and 1/2% increase in pet chance to dodge (also requires 2 points in Natural Armor)
-Grace of the Mantis: 2/2 for 2/4% dodge and hit chance

With the BM talents that would become:
+14% stamina, +10% health, +36% armor, +14% dodge and +40& healing

to hold aggro there are:

-Taunt*: 1/1 for taunt on a 3 minute CD (requires 2/2 Improved Growl)
and
-Improved Growl: 2/2 for 10/20% additional Growl threath.

While I definitely believe it won't replace a viable main tank, this can do wonders for emergency tanking situations or even as a viable off-tank.

I most certainly won't see myself getting into a group because of my pet's tanking capabilities, but I definitely see good potential in giving Hunters a little more viability in instances.

Pet Offtanking is going to be the new form of Crowd Control in WotLK, most likely. Think about it: Hunters can put their pet on one spare mob while trapping another. It'll be almost as great as a Mage's sheep.