The Helios Odyssey is a fan-less (quite) media hub enclosure supporting hard-drive sizes up to 1TB.
To watch videos stored on the Helios Odyssey you need an UPnP enabled Network Media Player, like the players offered by Helios: X5000.
Now with BitTorrent support you can schedule download task on the Odyssey box via a web interface and do not need to have you PC running all night.
Helios sells the Odyssey for $169 (you need to supply your own HDD) on their site. (Thanks Roy).