In interviews recently, Terry's mentioned he's been working on Long Earth 2, plus a Discworld novel. But as far as I'm aware, no details about said Discworld novel have been released yet. It may, or may not be, Raising Taxes.
There's also his autobiography, plus Science of Discworld 4, and of course the soon-to-be released Compleat Ankh-Morpork and Turtle Recall.
Unseen University Convivium 2012
University of Adelaide, South Australia, 6-8 July 2012