Feral Cat Advocacy Organizations
Alley Cat Allies is the "national [U.S.] nonprofit clearinghouse for information on feral and stray cats".
The Humane Society of the U.S. "...seeks a humane and sustainable world for all animals -- a world that will also benefit people." The HSUS produces a wealth of resources for feral cat advocates.
A must-read: the HSUS Position Statement on Trap-Neuter-Return
Neighborhood Cats ("the feral cat experts") is a New York City-based organization working to promote Trap-Neuter-Return (TNR) and educate caretakers and the general public.