Second Life:maps.secondlife.com/ (Just wait and if your connection quality to our Server is fast enough, a pop-up will appear.) Turn off ad blocking software as well
If you are having issues accessing the demos, here are some tips:
You need to make sure you have the latest and greatest java and flash installed. They are going to be moving to HTML5 soon so that will probably change in the future. If you have a laptop, run it in high performance mode. Also, run the game in the window. DO NOT switch to fullscreen. Some of the demos do have some sceen tearing, but it's not too bad. They look more native to me than OnLive. Also disable your ad blocking software. If you visit Walmart.com/gamecenter one of the demos might pop up as an ad.