American writers on board for Torchwood.
Jon Shiban, who wrote a good few X-Files episodes (none of them particularly good, but none of them awful either), and now works on Breaking Bad (best show on TV by miles).
Doris Egan, who worked on Dark Angel, House and Smallville, none of which I have seen, so I can't comment.
Jane Espenson, long time Whedon collaborator. Wrote a lot of Buffy, "The Replacement" probably being the only great episode. Wrote some awful ones like "Doublemeat Palace", too. Wrote on season 4 of Battlestar Galactica (which was pretty shit, although one of the episodes she wrote was a high point), and is show runner of the spinoff Caprica (which is average at best).
Also British writer John Fay, who wrote two episodes of Children of Earth.
And of course, Rusty himself is writing.