U.S.A.

Bebo
BlackPlanet (African-Americans)
Bolt (Music and Video)
Broadcaster (Video sharing and webcam chat)
CarDomain (Car lovers)
Care2 (Green living and activism)
Classmates (School, college, work and the military)
Dogears.net (US Universities)
Dogster (uh, dogs!?!)
Eons
Facebook
Flickr (pics)
Friendster
Graduates (School, College)
Golfspinner (Golfers)
Hi5
Joga (Soccer)
Kaneva (3D virtual world)
LibraryThing (Book Lovers)
eSpin (Teens)
Meetup
MiGente (Latinos)
MOG
MSN Spaces
MySpace
MyYearBook
Orkut
Piczo
Palopia (students)
Panjea (music, media player)
Passado
Reunion
Sconex
Tagworld
Travellerspoint (Travels)
Tribe
Vois
WAYN
Xianz (Christians)
Xuqa
Yahoo 360
Yelp
Zaadz (Change the World)
Zorpia
Doostang (Harvard, Stanford, MIT alumni)

Business Networks

CollectiveX (for groups)
Guanxi (China)
Ryze (USA)
Tianji (China)
Xing

Beyond USA

Arto.dk (Denmark)
ASmallWorld (Euro)
Cyworld (South Korea)
Epuls.pl (Poland)
EveryonesConnected (UK)
Faceparty (UK)
Fropper (India)
Grono (Poland)
Hyves (Netherlands)
IRC Galleria (Finland)
iWiW (Hungary)
LunarStorm (Sweden)
Mixi (Japan)
Nexopia (Canada)
Passado (Euro)
Playahead (Sweden)
ProfileHeaven (UK)
Rate.ee (Estonia)
Studivz.net (Germany’s Facebook)
Yeeyoo (China)
Yeskee (China)
Yonja (Turkey)

Anti-Social Networks

Isolatr
Snubster

Myspace Add-ons

Blingboo
Coshed
Gotomyproile
Modmyprofile
Myspacehive
Zobbler

Mobile Social Networks

mosh.nokia.com

If you know about other social networking websites, please post them in your comments.