Russell T Davies has been keeping this one very close, but with just a few weeks to go, the title of episode 12 of series 4 has been revealed:
The Stolen Earth
This will apparently involve “Earth’s greatest heroes” combating the “New Dalek Empire”.
It seems we’ll learn more about the Shadow Proclamation, which has been mentioned a few times, and it seems that an old enemy is waiting. Davros? I think so.