Kurt Cobain, Journals (2002)
The tortured soul that produced brilliant music was also a prodigious keeper of journals. This book reprints hundreds of pages selected from the twenty or more volumes of journals that Cobain left behind when he died in 1994. They may not provide clarity on his character, but they do provide an intimate window into his scattered thoughts.
Charles Cross, Heavier Than Heaven: A Biography of Kurt Cobain (2001)
This isn't a great book—it could have used an aggressive editor to tighten things up—but it is full of delicious (if arguably sensationalized) anecdotes that will interest hardcore fans.
Michael Azerrad, Come As You Are: The Story of Nirvana (1993)
Written before Kurt Cobain's death, Michael Azerrad's account of Nirvana's rise remains the strongest account of the band's history.