Although Second Life is currently the most participated in and widely virtual world out there, there are a number of equally interesting sites. The following well done article lists the most popular, along with active links, videos, and descriptions. Most of them share in common the thread that real money moves in and out, users are able to create and take ownership, and the users can manipulate them. Read more here ...

http://slgames.wordpress.com/2007/04/12/alternatives-to-second-life-uber-edition/#more-340