4. Richard Ayoade
I find the comedy elements of Doctor Who to be very important, something which you've surely noticed in this article by now, and will continue seeing. Assuming you finish reading this article. But it's because I value the comedy aspects of the show that I think Richard Ayoade would be an excellent choice. You may know him best as Maurice Moss on The IT Crowd, character that is the very definition of a stereotypical nerd - lives with his mother, is antisocial and afraid to talk to most people. But I think it would be wrong to judge his ability to play the Doctor based on that role alone. He has a variety of experience on other shows, even playing a rather antagonistic character in The Mighty Boosh ("How dare you speak to me of the crunch! You know nothing of the crunch!") One final point that I find to be intriguing is that Ayoade is an experienced director, having even tackled a full length motion picture before. Why do I bring this up? Simple... how cool would it be to have the actor playing the Doctor involved in the making-of process, even directing a few of the episodes himself? Still not convinced? See picture below.
I rest my case.