KDnuggets Social Bookmarking Tools
Social bookmarking sites allow people to store, classify, share and search bookmarks (also links and anything else on the web).del.icio.us and Digg are 2 of the most popular such sites, but there is a great variety of other sites (see e.g. KDnuggets 2007 Poll on Social Bookmarking.)
The "bookmark" button below
goes to addthis.com, which is a bookmark aggregator, allowing user to bookmark the page using del.icio.us, Digg, and many other social bookmarking sites.