ASPCApro -  The Humane Society' helps you resolve most cat behavior issues with the tools to correct the behavior. 

Cat Answer Tool -  Tools and resources for animal welfare professionals and volunteers as well as veterinarians, humane law enforcement and emergency responders.

CATegorical Care Guide - Cat Owner's Guide

Cat Care - ASPCA

Cat Diseases A to Z - Pet MD

Feral or Stray Cats - Alley Cat Allies

Maddie's Institute - Provides solutions to the most challenging issues facing the animal welfare community.

Pets WebMD - Keeping your cat healthy

Solutions to Community Cat-Related Issues - from Best Friends Animal Society

Virtual Pet Behaviorist - ASPCA