Ms. Kline Online

Social networking web sites allow users to create online accounts, post content, and to communicate with other users.

Read about social networking web sites in Wikipedia!

List of social networking websites:
http://en.wikipedia.org/wiki/List_of_social_networking_websites

Example of an education-related social networking web site:
http://www.classroom20.com/

Twitter
Social network

Ning
Free Social Network Software