Diigo is a social networking site & tool that is similar to del.icio.us What Diigo adds though is the ability to annotate websites. You can highlight & add notes & questions to a website and share both the site & your thoughts with others. If you still love del.icio.us because of its great RSS capabilities, like I do, don't worry. Diigo & del.icio.us play well together; when you "Diigo something" it also gets added to your del.icio.us account, tags & everything.

 Don't take my word for it! Watch this great video created by teacher Clay Burell. He makes a pretty good case for using the web as your textbook. Enjoy!