
And to clarify for anyone new -- a permanent buff means the buff will not be lost upon death if the creature dies in the wild or as your pet. A fragile buff will (or if you die with the pet out!).
ALL BUFFS WILL BE CLEANSED IF A PET IS TAKEN INTO AN ARENA OR A RATED BATTLEGROUND.
Permanent Buffed Pets
Armored Battleboar - Retains fire across its body if hit with a torch from a Tauren starting quest.
Mining Monkey - Carries a pickaxe (Dungeon pet)
Consumed Thistle Bear - Purple glowing aura.
The Lone Hunter - Sword through the head.
Angered Arakkoa Protector - Blue mist.
Oiled Fledgeling - Black, thick, oily coat.
Oil-Stained Wolf - Black, thick, oily coat.
Kung Din - Rotating chain around his neck.
Grainhunter Hawk - Can be tamed with dull skin. It can also be tamed holding a bag -- the bag is fragile and will be lost upon death, but the dull skin will be retained.
Corrupted Crane - Sha effect around its feet and a dull body.
Ik'thik Terrorclaw - Sparkling, smoky Sha effect.
Coldbite Matriarch - Grey body, sha streaks come out of her eyes.
Amberscale Basilisk - Grey.
Furious Goat - Has the murky ground effect of the Sha tigers, coupled with sha 'spirals' that frequently float around it. Roam in packs, Sha must be up near the burlap trail, on the spawn point next to the hozen camp. Best advice is to hide behind him and trap a goat as they ride around -- you can kill the riders atop the goats without aggroing them. (Thank you Amber and Qi!)
* It should also be noted, as some have asked, that the Sha buff on the goats is NOT a damage or health buff in any sort of way. I've checked in triplicate, both on wowhead and in practice. He, frankly, probably hits for less that some of my other pets.