This has most likely been suggested before but I haven't seen it implemented yet so...
The only pet with a real use is the horse, well mayeb all the pets should give a bonus for raising them
I was thinging something like
Horse-> speed(we know)
Monkey-> sustenance+ (They make bananas?)
Yoda-> wisdom or int+ (yoda is very intelligent mind you)
Squirll-> charme? (couldn't think of really anything good, but they are cute so maybe people will like you better if you have one)