One of the big announcements at MIX this year was Silverlight Streaming, which you can find at http://silverlight.live.com/. 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 http://dev.live.com/silverlight/. 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: http://silverlight.net/quickstarts/.