Free Online Social Networking Sites and Tools

Ning

Twitter

Facebook

Jaiku

TakingITGlobal

ePals

stinto - free online chat tool.  Can be added to blogs, etc.

imbee

Edmodo - free, private microblogging for educators.   Edmodo provides a way for teachers and students to share notes, links, and files.

Nabble - free forum and other embeddable apps

Blip.fm - social networking through song lists.  Neat!  Can be linked through Twitter.

Learn Central - Social network for educators

Slinkset - Social news sharing.