I just finished reading Kate Remembered, by A. Scott Berg. Published in 2003, the year of Katharine's death, this book is beautifully written by author as well as decades long friend to Kat. Scott writes not only about her life, but about their time together as friends. As a biography written by someone who knew Kat to the fullest, you learn about her opinions on almost everything (naturally), as well as details about her life including Howard and Spencer that she normally didn't share with the public.
I must say I was sad finishing this, not only because it was such a good read, but because at the end, you get to know her a little bit closer, and understand how much she lived it up.