I've posted a couple before. Here are the links. Keep in mind that, as the Hound pointed out, a lot of it is somewhat arbitrary: what abilities to give a demon, what physical stats give an animal... judgment calls all of them.
Titivillus, patron demon of calligraphers
Arisitis, a magical ermine (incomplete, but somewhat detailed)
Our saga also added a miniature dragon and a magical gerbil (!) as magical animal companions. I'll post the stats when I grab the sheets off the players. 