No Kidding
No kidding! is an all-volunteer, non-profit social club for couples and singles who, for whatever reason, have never had children.
http://www.nokidding.net/
VHEMT
Voluntary human extinction movement. may we live long and die out. thank you for not breeding.
http://www.vhemt.org/
World Population Awareness
World overpopulation awareness is a non profit organization that endeavors to make people aware of population, overpopulation, its impacts, and what the choices are in doing something about it.
http://www.overpopulation.org/