If you would like to promote your websites and share information with other surfers, then you might want to join a few of these social networks. That way you will also create a few natural links to your web sites and to your favorites. (And you can create networks of friends and business contacts by placing a link to your abbreviated Facebook profile -- for example, http://www.facebook.com/people/David_Maxwell/633321643.)

The networks (and when I find and join new ones, I list them on http://twitter.com/affiliatebin):

Bebo
bizpreneur
Blogger
del.icio.us
Digg
Facebook
Flickr
FriendFeed
Friendster
Jaiku
Jumpcut
Kiva
Last.fm
LinkedIn
LiveJournal
Multiply
MyBlogLog
MySpace
Plaxo
Second Life
StumbleUpon
Squidoo
Technorati
The DJ List
Tumblr
Twitter
Upcoming
Yahoo Answers
Yelp
YouTube

Update, 23 April 2008: Wikpedia has a good list of social networking sites.