Social Bookmarking

Diigo - www.diigo.com
Delicious - www.delicious.com

Tutorials:
Video tutorials on Diigo - great info
Social Bookmarking in Plain English - great info
Social Bookmarking Making the Web Work for You - great info
Social Bookmarking with Delicious and Diigo for a Law Library

Links:
Annotating and Sharing Links With Your Students
Taxonomy