About.com Vet Medicine- Good information about pet health and medications.
http://vetmedicine.about.com/

Adoptapet- A must-see website for anyone looking for a companion.  Lots of good advice for selecting and protecting a pet.  Includes instructions on how to link them to your website.  They also offer a banner.
http://www.adoptapet.com/

Animal Poison Control – ASPCA (American Society for the Prevention of             Cruelty to Animals)
http://www.aspca.org/site/PageServer?pagename=pro_apcc

Dog Infomat- A large website with many dog-related links to health, breeding, etc.
http://www.doginfomat.com/

Humane Society- A major clearinghouse for animal protection information and government policy.
http://www.hsus.org/

Pet Place- Tons of information about cats and dogs.  Alto retail sales of pet products.
http://www.petplace.com/