Spaying and neutering owned and stray cats is the single most important step you can take to reducing pet overpopulation and suffering.  Below are some low-cost veterinary resources in the Philadelphia area, including both clinics and discount certificates — some clinics also offer low-cost pricing for vaccination and FIV/FeLV testing. Please note that some are appropriate for ferals and strays, and others only for owned pets:

Philadelphia Community Cat Council
PCCC offers low-cost clinics for feral and free-roaming cats at the PSPCA Cube Clinic. Clinic dates, prices, and contact information are listed on the PCCC website — be sure to contact PCCC ahead of time to schedule your cat.

PAWS Spay/Neuter & Wellness Clinic
The PAWS clinic, located on Gray’s Ferry Ave in Southwest Philly, offers low-cost spay/neuter and other veterinary care by appointment. PAWS also offers a low-cost vaccination clinic twice per week (no appointment needed). Currently (as of January 2013), PAWS is offering FREE cat spay/neuter for residents of zipcodes 19143, 19145, and 19146 who receive any form of public assistance (Medical Assistance, food stamps, TANF, SSI, etc).

The Spayed Club
The Spayed Club offers grants and discounts for spaying/neutering to low-income families with an annual income of $25,000 or less. They also host a low-cost spay/neuter clinic in Sharon Hill (Delaware County, about 15 minutes from West Philly).

Hope Animal Sanctuary
Hope Animal Sanctuary offers mobile spay/neuter services to cats and dogs owned by low- to moderate-income Philadelphia residents. No ferals. Advance registration is required. Clinic dates, locations, and prices are available on the Sanctuary’s website.

Forgotten Cats
Forgotten Cats of Delaware offers clinics in Claymont, DE and Willow Grove, PA. Clinic dates and prices are available on the website.

PSPCA Wellness Clinic
PSPCA offers low-cost veterinary services including spay/neuter and vaccinations, as well as general care.  It is a walk-in clinic, serving the community on a first come, first served basis.   Call 215.426.6300 for clinic hours and more information.

Animal Welfare Association of New Jersey
The AWA clinics are open to all members of the public, regardless of residence or income. Open to owned pets, friendly strays, and ferals any day of the week — no appointment needed for strays/ferals except on Saturdays. Contact AWA for more information and pricing for strays/ferals.

Morris Animal Refuge
Morris Animal Refuge offers a $40 spay/neuter certificate that qualifies you for a discount at many local vet offices. Girard Veterinary Clinic will spay/neuter for free when this certificate is presented, and the Morris website provides a list of other participating veterinarians.

Spay and Save
Offers discounts to pet owners and rescuers in need of financial assistance at participating veterinarian offices. Application is required.

Friends of Animals
FOA offers a certificate (available for purchase online) for low-cost spay/neuter. Prices and participating veterinarians are available on the website.

Cats in Crisis
Cats in Crisis helps cats and kittens with special medical needs receive the veterinary treatment they need. The organization assists those who might otherwise have to euthanize a cat with medical issues due to lack of funds.