A grab bag of stuff, obviously, some of it tied to the year's Doctor Who. Stats for new characters and monsters, adventures based on hooks the series dangled, GMing advice on interesting topics it brought up.
So for example, the DWAITAS Annual 2012 might include...
An introduction to RPGs, just in case. A short solo adventure, character sheets for the Doctor, Amy and Rory, just enough info that a new GM could pick this book up if they got it for Christmas instead of the boxed set.
The Silence - stats for the creatures and the cult, rules for EyeDrives, and an article on UFO lore and history and their place in it.
The Corsair - stats for all nine incarnations would be a bit much, but a page or two on him/her?
The Flesh - stats for their various mutations and advice on how to use doppelgangers in a game. With a sidebar about the Teselecta.
A Good Game Goes To War - stats for the Doctor's superhero teamup.
Adventures - a nice straightforward one relating to one of the asides from this year like the Doctor escaping from Colditz, and a Christmas Special because this is in shops in time for Christmas.
And thirteen half-page adventure hooks because that's a good tradition to keep up.
(And as suggested, I am now wondering what I'd put in The Door In Time Annual...)