Doctor Who Crossover?

Have you ever thought about a crossover of Doctor Who or Torchwood with another TV show?

It would be really cool to mix some shows with Doctor Who. One that comes to my mind is Spooks. I don't know if you know it but it's also a BBC show about the MI5. It would be really fun to watch Harry meet the Doctor (I think Harry is still on the show but I'm not so up to date with the episodes).

Most crossovers with other shows are in FanFics. I read a couple of really good ones and wrote one or two myself (no Doctor Who one).
One I really like is a Torchwood/Blood Ties crossover written by Helen Pattskyn. It is called "Blood Moon Rising".
But you can find a lot of other crossovers when you have a look at fanfiction.net where you find the section browse crossover fanfiction.

Is there a show you would love to see in a crossover with Doctor Who or Torchwood?
Just leave me a comment and tell me what you think.