It starts off with Sam Vimes going away on a two week holiday (with his wife Sybil) to their country house. The working title is Snuff (meanings: fine ground tobacco, snorted up the noise; to 'snuff' out a candle, leading to 'Snuff' films depicting actual death)
Announcement from Pterry and my awesome Squidoo lens about the City Watch, Goblins and snuff.
He is also going back to another, previously secret, project, put aside when the Discworld series took off. Two unpublished novels* in a series called The Long Earth. The Long Earth is science fiction, and he'll be collaborating with Stephen Baxter. (Actually, that's not as surprising as it originally seemed - his Science of the Discworld books and the early Johnny and the Dead series definitely edge right into Scifi territory).
*one full-length story and one with two short stories. This gets a little confusing!
The most recently published book is I Shall Wear Midnight.
The fourth in the young adult series following the young witch Tiffany Aching as she tramps in her giant boots from her shepherd roots on the Chalk, up to Lancre and back, attracting unfortunate allies with minds of their own, and the flattering and even more unfortunate attentions of Winter itself and Granny Weatherwax, It was published in September 2010 and I've already reviewed I Shall Wear Midnight in some depth here!