Interesting collection of possibilities on TVGuide.com.
Doctor Who: Who Should Be the Next Doctor?
They also list some pro's and con's for each possibility. [I mentioned Andrew Potts, the person in the last photo, when I first heard Matt Smith was leaving.]
Interesting lineup.
I like the ideas of Natalia Tena and Andrew Potts, as well.
Rupert Grint!? The Doctor is a ginger at last - and a Weasley...