I've had some success with Lil' Deathwing. He can open with Elementium Bolt, buff its damage with Roll, then Tail Sweep. At the end of Tail Sweep's turn, the Bolt hits, dealing massive damage. It'll usually knock out the opposing pet, but if not, it'll stun them for a turn and more than likely proc Lil' DW's Dragonkin ability, allowing the next Tail Sweep to deal pretty massive damage with no risk of counterattack. Lil' Deathwing's a pretty slow pet, too, so you're almost always going to be able to take advantage of Tail Sweep's bonus damage.
Another high burst pet combo I've noticed is anything with Chew. Your pet takes a turn to chew grass, then, at the end of the next turn, will deal a lot of damage. With a one turn cooldown, it's a pretty devastating, repeatable combo. You can also switch out and still deal the damage, in case your grass-chewing pet is ever in danger of dying.
I've also been able to use the spider pets successfully. Most of them have the same moveset, but I'll use Feverbite Hatchling as an example (since that's the rare quality spider I caught first). Brittle webbing combined with Leech Life is very useful for stalling, not to mention the fact that the former is very effective against attacks that hit more than once. Brittle Webbing will also reflect damage on DoTs. Anything with damage reduction shields will counter it, but the double healing from Leech Life is still pretty sweet (AND Brittle Webbing lasts one more turn than Sticky Web - at the cost of its root, it seems).