Some renowned composers who are writing music these days: Elliott Carter (by the way, happy birthday, Elliott, in december 11 you'll be 102 y.o.), Milton Babbit (almost centenarian), Phillip Glass and Tan Dun. I not completely sure but I guess that some great composers who passed away recently such as Ligeti, Stokausen and Xenakis it's probably that they wrote something in the XXI century. Boulez is still alive but according my information, he didn't write anything new for the piano since more than 50 years ago.