
Miro is an open-source video aggregator and player, developed by the non-profit Participatory Culture Foundation. Their purpose is admirable:
The software itself comes in Mac, Windows, and Linux flavors and will download and play nearly every video file format a person could reasonably want to watch. The system works as something like a DVR crossed with iTunes (but without all that annoying drm), allowing users to scan multiple sources for video podcasts, available torrents, and even YouTube pages which it then downloads and holds ready for you to watch at your convenience.
For the content that is subscribable (video podcasts), they have set up specific channels, one of which is a Science channel with content from over 70 different shows, including the Discovery channel, NASA, and many smaller independent producers. For my older son, who is an avid budding chef, I've already subscribed to the Food Science video podcast (in HD, even). Take a look - it certainly seems like a much better range of content that is available on the TV after school.