Aries: A dog! Energetic, active, and playful; what's not to love?
Taurus: A turtle; they're not too energetic, can take care of themselves for the most part, and are absolutely adorable.
Gemini: A talking parrot; especially one that can be trained to crack jokes.
Cancer: Puppies or kittens. Anything small, adorable fluffy, and a baby.
Leo: A big, bold, and ferocious feline.
Virgo: A cat: Adorable, affectionate, and independent.
Libra: Hm, good question. One the one hand, a dog is active, affectionate, and companionable. On the other hand, a cat is pretty independent and won't require as much time and attention. Oh, I don't know. What would you do? Are you sure?
Scorpio: A cat. Secretive, mysterious, and unpredictable. What's not to like?
Sagittarius: A horse, of course! Let's hope it's got enough stamina to keep up with me.
Capricorn: Do I have to pay for it?
Aquarius: A hamster. First, I've got to set up a detailed cage with tubes going from here to here, and an energy sensor-they don't make anything like that? That's okay, I'm sure what I come up with will be much better.
Pisces: Fish. When their owner forgets about them for weeks on end, they're easy to replace. If they remember to replace them...