Roku is currently in the process of adding Amazon video-on-demand on its little set top box. The support is currently being tested as a private beta (which unfortunately has reached its limit) and is expected to be available with firmware 2.0. Of course, there is no info on any expected release date as to when this feature will be available to all users. One uncertain factor is whether the service will be in standard or high-definition or better yet, both.
This is certainly a move in the right direction for Roku, with Netflix already streaming, the additional content that will be available from Amazon is sure to keep just about anyone busy with plenty to watch.
Additionally, if you check out the image (to the right) it appears to have a YouTube logo along with Netflix and Amazon, which would lead us to believe that support will come along with the next firmware version.