FOSTER & ADOPT
Zillow New York pet-friendly page with over 18,000 pet-friendly listings with fair rental price estimates.
Trulia New York apartments page with over 14,000 listings in Manhattan alone with pet-friendly filters and in-depth neighborhood information.
Hotpads New York apartments page with over 29,000 listings with pet-friendly filters and in-depth photos, information, as well as unique features such as street view.
RentCafe New York page with numerous pet-friendly listings. Check out their Renting with Pets: The Ultimate Guide for more information.