I don't seem able to write an entire book without a dog in it. Always a dog, rarely a cat, never anything else. Maybe that's because in the last 16 year, we've had anywhere from three to six dogs living in our house at any given time -- all rescues. Since living in the country means a mouse problem, we've tried to have cats, but the first chance they get, they escape and never come back.
I just can't imagine life without animals in it. All my friends have pets. I don't completely trust people who don't have them. The simple fact of caring for a dog tells a lot about you to other people.
My favorite of my own literary pets: Elizabeth and Bear from Criminal Deception. Better known as Olivia and Chance in real life. And yes, they really are that ornery.