During an interview at TIFF this past week, George R. R. Martin revealed a partial chapter from The Winds of Winter, the next book in the Song of Ice and Fire series.
The chapter is centered around Victarion, which the author begins reading at the 30:50 mark in the above video. This chapter follows one he previously revealed in December 2011, centering on another Iron Islander, which you can still read here. While not necessarily a never-before-revealed chapter since GRRM often reads from his works-in-progress, the interview does provide a wonderfully clear recording of it.
Naturally, spoilers for the entire published series abound.
Stubby the Rocket is the mascot of Tor.com and would love for GRRM to write a passage describing it as it sails through the stars....