Here is his obituary at The New York Times.
Facebook is filling up with thoughts about Hizzoner. Via The Lower East Side Preservation Initiative:
His term corresponded to the 1980s artistic renaissance in the East Village and, not coincidentally, the first giant wave of gentrification. His often brash, contentious, energetic and multifaceted personality seemed to many to personify the character of the city itself.
Several people have sent along this interview with The Daily Beast from 2010... in which Koch discusses the Tompkins Square Riots of 1988...