IBM has
recently announced an interface for Second Life for the blind. The system runs in Firefox (supposedly - I couldn't make it work) and presents standardised buttons for core functions (also accessible by hot keys) and a textual interface that is designed to work smoothly with screen readers.
Sighted people can also add descriptive text to objects so when the user is navigating around in Second Life they can stop and examine notes about the objects that they see. The sighted users are also encouraged to add spoken notes as well.
I'd love to give you more detailed feedback of the system, but I can't get it to work... However I grabbed a screen shot of it waiting to log in (I can it to work to that point).. The pane to the right stretches down and to the right to fill a decent sized browser window to give you a reasonable size.