Following are links that may be useful to you:
Animal Welfare/Education
http://www.aspca.orghttp://www.petfinder.com
http://www.hsus.org
http://www.fundforanimals.org
http://www.theanimalspirit.com
http://www.wspa-international.org
Medical Information
http://www.avma.comhttp://netvet.wustl.edu/vet.htm
http://www.inno-vet.com/
http://www.vetcentric.com/
http://www.vet.purdue.edu/~lamarch/mainpage.htm
http://www.vet.utk.edu/hnilica/index.html
http://www.uga.edu/~lam/kids/ (for Kids)
Behavior/Training
http://www.petfinder.orghttp://www.petbehaviorproblems.com
http://www.pethelp.net/
http://www.pbs.org/wgbh/nova/vets/
http://animal.discovery.com/fansites/e-vets/yelpline/yelpline.html
End of Life Issues
American Veterinary Medical Association Pet Loss Pagehttp://www.avma.org/care4pets/avmaloss.htm
Association for Pet Loss and Bereavement web site
http://www.aplb.org/
Dealing with Grief
http://www.teleport.com/~twscan/Pages/Grief.htm
Grief and Pet Loss by M. Mums DVM
http://www.petloss.com/muns.htm
Ideas for Dealing with Loss of a Pet
http://www.foreverpets.com/B%2DPetLossTips.html
Pet Loss and Bereavement Resources (Delta Society)
http://www.deltasociety.org/dsn000.htm
Pet Loss Support Page by Moira Anderson Allen, author of Coping with Sorrow.
http://www.pet-loss.net/