Well most of the good ones you have to download...however here are some; -Habbo -club penguin -moshi monsters -ourworld -prepectual kid -Meez -groovy girl
This are some: www.ourworld.com www.habbo.com This ones are really good... they are for teens. The next ones are for kids but you can try them, they are fun as well and without any downloading! ;D...
Try Xivio.com, its a free 3D virtual world! No download too! My favorites are: www.clubpenguin.com www.virtualfamilykingdom.com www.dizzywood.com www.whyville.com www.habbo.com www.moshimonster.com...
go to www.bebo.com and then add the app MiniPlanet (it probably won't come up in your bebo search criteria so search www.google.ie and it will almost definitely come up there)