Twitter: Blogging and Instant Messaging come together in 140 characters to create Twitter.
Twitter in Plain English by Common Craft
Great guide to using Twitter but has lots of ads.
Twitter clients:
Twitbin (Firefox extension)
Plurk - like Twitter, but can create conversations easier.
Ning:
Social Networks I belong to:
EdubloggerWorld: http://edubloggerworld.ning.com/
School 2.0: http://school20.ning.com/
Classroom 2.0: http://www.classroom20.com/
Teaching 'N Technology: http://teachingntechnology.ning.com/
Social Networking in Plain English by CommonCraft
sc_project=3541840; sc_invisible=1; sc_partition=39; sc_security="d5fe242f";