If you are interested in social bookmarking, you may wish to take a look at some of the following sites:
http://del.icio.us/
http://digg.com/
http://reddit.com/
http://www.stumbleupon.com/
For a more complete list of social bookmarking sites, check out the following Wikipedia page:
http://en.wikipedia.org/wiki/List_of_social_software#Social_bookmarking
If you have other resources, ideas, or questions about social bookmarking, please let us know by replying to this thread.
Steve