Self Defense, a four-disc boxed set of remixes from the Never Never Land album, on September 12. But it appears only three (!) tracks are previously unreleased, so I think I may skip it.
Tons of new remixes, none of which are available in the US, even on iTunes: I would especially like to hear Depeche Mode’s "John the Revelator (UNKLE Re-Construction)", and Massive Attack’s "False Flags (UNKLE Surrender Sounds Session #2)"
Wikipedia notes UNKLE’s new album The Future is Unwritten is due sometime this summer (with a teaser on the official site).