SitePretty interesting. So far its in beta but will eventually be released to everyone. Right now it only works with TF2 but it seems like it will be updated to support all of Valves games. In the FAQ it mentions that if you go so far as to replace all maps, textures, sounds, etc and make a 100% custom movie using the tools, there is no restriction on what you can do with the final output. You could even sell your movie.
Of course most people don't have the animation skills needed to make something decent, but still.
