I learned about the Hillywood Show when watching them give an interview on TheOneRing.net's TORN Tuesdays weekly show. They are absolutely fantastic and ran a contest for fans to react to their Doctor Who Parody music video. This is a mashup to just a few of the reactions I found. Please check out their channels! My favourite reaction is at 3:29 ;p
This is a transformative work under youtube's "Fair Use" policy and uses the juxtaposition of clips to provide a commentary. Full credit is given in the annotations I have linked to at the beginning of the video, and to the awesome Hillywood Show.
Royalty Free Music: Coyote Kisses - Six Shooter