Microsoft today launched the Xbox Video on the web. https://video.xbox.com/ will let you browse through Xbox Video Store and search your favorite videos. You can both buy and rent movies and videos from the web interface. Not only you can buy them, you can stream directly within your web browser. The only drawback is that you won’t be able to stream the videos in HD. Microsoft is expected to release a Windows Phone app for Xbox Video service in the coming weeks.
Check out Xbox video on the web here.