Microsoft is currently offering Microsoft Expression Encoder for a free 180 day trial complete with support for Silverlight as described in previous Tips of the Day hand, as shown in various Learning Videos.
To download your free copy, go to the Silverlight site and click on Get Started. Scroll down to Designer Tools and click on Expression Encoder. Note, the initial licenses is for 60 days, but the directions on the download page include a trial product key that extends the license for 180 days.