Christmas Special: A Christmas Carol by Steven Moffat
Amy and Rory are on their honeymoon during the episode, and run into trouble when the pleasure cruise spaceship they’re travelling on finds itself under attack from “something very nasty”. The spaceship is orbiting an alien planet, which is where the Doctor is for a considerate part of the story. This therefore causes Amy and Rory to be separated from the Time Lord for the majority of the episode.

Series 6: Episodes 1 & 2 by Steven Moffat
River Song appears in the opening two-parter, which is set in 1960’s America. Doctor Who Magazine says "speculation is mounting that River, who in the future is serving time for killing "a hero to many", may be responsible for the assassination of President John F Kennedy! Although probably not".

Some of the storyline is also revealed:
"The story sees the Doctor and his friends answering a secret summons that takes them on a continent-hopping adventure from the desert in Utah all the way to the Oval Office of the Whitehouse in Washington DC"
The list of confirmed cast members for these episodes can be found here.

Series 6: Episode 3 by Neil Gaiman
In this episode, the TARDIS breaks down on an alien junkyard world, which is where the Doctor encounters Idris (played by Suranne Jones).

Idris is preparing for death when the story begins, but lives and "by the time the Doctor and friends meet her, she’s gone mad and ends up biting the Time Lord. . . but not on the bum, DWM can exclusively reveal".

Doctor Who Magazine then elaborates on the character of Idris:
"It’s rumoured Idris and the Doctor have met before, so who could she be? A new incarnation of the Rani, perhaps? Maybe the Master? Or a future version of the Doctor him. . . er, herself?"

Series 6: Episodes 5 & 6 by Matthew Graham
Steven describes the episodes as "a thrilling and terrifying two-parter" and says that "the Doctor will face a dilemma the like of which he’s never seen before".

This month’s Production Notes takes the form of a conversation between Steven Moffat, Matthew Graham, Beth Willis and Marcus Wilson (producer of Block Two, and "the opening two-parter of Series -um- Thingy") Here’s an interesting segment:
Steven: Leela never met the Daleks.
Beth: Sorry, what?
Matt: Yes, she did. Of course she did.
Beth: What are you talking about?
Steven: The scene in the second half. Where the Doctor’s having flashbacks.
Marcus: Before he dies?
Steven: Yeah, before he dies. It says he’s remembering being with Leela on Skaro.
Matt: Yeah, on Skaro, with Davros. No, Sarah. I’m thinking of Sarah Jane.

Episode 4 of Series 6 will be written by Mark Gatiss. Steven Moffat will write Episode 7, which is the first episode of a two-parter that will be concluded in the Autumn with Episode 8.

Taken from Life Doctor Who and Combom