There is now a preview of the forthcoming series running on a loop on BBC's Digital service; the loop runs for about a minute and a half and features clips from a number of stories. Beware spoilers!
The preview is available on Sky Digital and Virgin Media but not on Freeview because of scheduling reasons, according to the official Doctor Who website, which says it hopes to have the trailer on the site shortly.
Update - this preview is now available via the BBC channel on YouTube.
A number of clips are shown, including brief snippets from later stories such as Human Nature (including the wedding reported in Heat and on tonight's Graham Norton Show), Utopia and The Sound of Drums, featuring Derek Jacobi, Michelle Collins, John Simm and John Barrowman.