This screenshot of Electric Sheep's work on a virtual world in the browser is nice looking. They're using Ogoglio for the sever component and Papervision3D for the client. The look is nice certainly. When I was in Arlington this past week, Jesse demoed some Papervision stuff to me, and I was certainly impressed. This from ESC continues to impress. Of course, this is no where near what Second Life is -- a single night club in no way compares to an expansive and varied virtual world -- but it is impressive for a low barrier to entry alternative that runs in the browser.