Apple iTunes is currently offering selected science fiction series premiere episodes for free. "For a limited time, download the first episodes of these series for free and own their first seasons for a great price"
Included in the offerings is Doctor Who (Rose) and Torchwood (Everything Changes (both SD and HD versions)). Other series include the recently re-imagined Battlestar Galactica series, Fringe, Heroes, Stargate SG-1, Eureka, Supernatural, Buffy the Vampire Slayer, The X-Files, Stargate Atlantis, Robin Hood, Star Trek: Enterprise, and Star Trek: Deep Space Nine.
Again, we don't know how long this will last as it only states "for a limited time" - so get them while you can.
Links to episodes: