Some popular 3D online virtual worlds are:

Blaxxun Interactive ( http://www.blaxxun.com )

Traveler ( http://www.digitalspace.com/index.html )

Active Worlds ( http://www.activeworlds.com)

MEET3D ( http://www.meet3d.com )

Palace ( http://www.thepalace.com)

Virtual Places ( http://www.vpchat.com )

Worlds ( http://www.worlds.net )

Microsoft Chat ( http://www.mermeliz.com )

Vzones ( http://www.vzones.com )