One of the big announcements at MIX this year was Silverlight Streaming, which you can find at I haven't tried it yet, but it looks pretty cool. The terms of use are listed at the bottom of the page--basically, while the service is in pre-release mode you can host up to 4Gb of content for no charge.

If you want to try it out, you'll want to check out the developer page on Since the service hosts Silverlight applications, you'll need to build at least a simple one of those. There are some good quickstarts to get you up and running here: