While this isn't filk exactly, it's music for a fantasy game: Skyrim. I haven't ever played it, though my sister tried to talk me into it a few months ago. I got sucked into SW: The Old Republic instead. But one of my friends on FB linked to this video of Peter Hollens and Lindsey Stirling doing their adaptation of the Skyrim theme song.
With one voice and one violin, they created 120 tracks that they put together for the full song. Then the two of them did some filming to create the amazing video to go with it. Awesomesauce with coolness on top.
As soon as I pick up another iTunes card, I am so picking up the song. Then I'm probably going to buy the Skyrim soundtrack. Some of these MMOs have great music tracks for writing to. I've already got one of the World of Warcraft CDs. This will make a great addition to my collection.