http://reddit.com http://del.icio.us/ http://digg.com http://stumbleupon.com http://www.connotea.org/ http://www.contentpop.com/ http://fark.com/ http://www.feedmarker.com/ http://feedmelinks.com/ http://www.gibeo.net/ http://www.google.com/bookmarks/ http://www.gravee.com http://www.hypediss.com/ http://www.iliketotallyloveit.com/
you could have used the search function. At the end of this thread http://forums.digitalpoint.com/showthread.php?t=499386&highlight=list+bookmarking+sites there'sa link to a list of 500.