A Ning is an online environment that allows you to create your own social network that is centered around a desired topic.  

Education-based Nings you might want to follow:

EdWeb.net

The Educators PLN Ning

ICE 2010 Ning

ISTE Community Ning

Smartboard Revolution

Classroom 2.0

Art 2.0

Gifted Education 2.0

School 2.0

ASCD Edge

How to create your own Ning network.