Social Networking 

Twitter: Blogging and Instant Messaging come together in 140 characters to create Twitter.

Twitter in Plain English by Common Craft

Twitter Guide:

Great guide to using Twitter but has lots of ads.

Twitter clients: 

Twitbin (Firefox extension)

Twirl

Snitter

Twitterfeed

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";