Well, Monster of Legend and Paragon are solid starts. For a smaller boost, Warbeast, Horrid and Magebred are all templates that keep the animal type.
Otherwise it really depends what you're going for on the OHGODWHY scale. Any thing from Advanced Dire Bat to Advanced Horrid Magebred Warbeast Shadow Corpse Creature Hivenest Swarmshifting Dire Bat.

As for plants, I do love running packs of Shocker Lizards or Arrowhawks with Shambling Mounds. I've also seen pretty epic things done with cracked out Assassin Vines.
This site http://monsterfinder.dndrunde.de can help as well.