I have been meaning to get together a list for a while so took some time today to tour and pick up Landmarks - I posted the list on the MuniGov Second Life page: http://sites.google.com/site/munigov20/Home/second-life
You might be particularly interested in the Alameda County site - it has a polling place laid out. I just found it today while I was messing around in there.
If I find more, I will put them on the site. Hopefully I will get a chance to do a write up of them for my magazine (GridWorks). It would be helpful to have a listing and article about each. If anyone knows of any I missed, just let me know or you can add them directly onto the page if you have signed up on the MuniGov site.