Lively (http://www.lively.com)

Some sites make setting up and traveling within a virtual world complicated, and in return very frustrating. Lively.com has taken away some of the annoyance by making the process of creating your own room really easy and by offering individual rooms for teens to explore one-by-one (although it's still annoying that the site isn't available for Macs just yet). The room possibilities are endless and the avatars' activities (dancing, shaking hands, throwing up) are more than most sites, but there's not a lot of choice when it comes to the avatars themselves; at launch, there were only three female options to choose from -- all of which looked like Angelina Jolie on steroids. The site still has some kinks to work out -- like the occasional computer freeze from playing, faulty avatar movement, or the inability to move certain pieces of furniture around -- but if users learn to be respectful toward one another, Lively.com can be a fun way to dip into virtual worlds.