Digg.com:
This site concentrates almost entirely on web-based news items and site links. Registration is simple and personal profiles less prominent.
del.icio.us:
Primarily set up to enable registered users the ability to store all their favourite web links on the internet.
Facebook.com:
All information on Facebook is orientated from your own personal webpage however privacy settings enable users to control both the content and who has access to your page.
Twitter.com:
All information on Facebook is orientated from your own personal webpage however privacy settings enable users to control both the content and who has access to your page.
Reddit.com:
Displays lists of categorized websites and news stories and enables registered users to compile a list of their own bookmarked sites. Registration only requires a username, no email address or other information.
Stumbleabout.com:
Enables registered users to bookmark web links. Once an interest is registered, users will be sent links to similar pages.