Diigo is a social bookmarking site that is really giving the current champion, del.icio.us, a run for its money. It does everything that del.icio.us does (including simul-posting to your current del.icio.us account!) and so much more. From highlighting on a page, to adding sticky notes, to sharing bookmarks with groups, it really turns websurfing from a passive experience to a highly active one. Jennifer Dorman created the DEN group in Diigo a little over a week ago and there’s already over 50 members!