general
American Animal Hospital Association (AAHA)
American Association of Feline Practitioners (AAFP)
The American Society for the Prevention of Cruelty to Animals (ASPCA)
The American Veterinary Medical Association's "Web Page on Animal Health"
Best Friends Animal Society
Cornell University Feline Health Information
Doris Day Animal League
Feline Advisory Bureau
The Humane Society of the United States (HSUS)
PaLC (Prevent a Litter Coalition)
Pennsylvania Veterinary Medical Association
Spay/USA
World Animal Net Directory

feral cats
Alley Cat Allies
Neighborhood Cats

poison information and resources
American Veterinary Medical Association list of poisons
ASPCA Animal Poison Center
Cornell University Poisonous Plants Database
University of Illinois Veterinary Medicine Library
University of Pennsylvania's Poisonous Plants Home Page

puppy mills
Central PA Pet Store Protest Website
Hearts United for Animals
Prisoners of Greed
Stop Puppy Mills