From the Times Online:
David Tennant is to quit as Doctor Who at the end of next year.
Tennant took up the role as the tenth incarnation of the Doctor in 2005, and will end his tenure after filming five final episodes, the last of which will be shown early in 2010.
He said: “I’ve had the most brilliant, bewildering and life-changing time working on Doctor Who. I have loved every day of it. It would be very easy to cling on to the Tardis console for ever and I fear that if I don’t take a deep breath and make the decision to move on now, then I simply never will. “You would be prising the Tardis key out of my cold dead hand. This show has been so special to me, but I don’t want to outstay my welcome.”
More @ Tennantively.Org
The video in where he accepts his award and makes an announcement can be found at Tenn Media.