Not sure if these have been mentioned...

Original Gangstas: The Untold Story of Dr. Dre, Eazy-E, Ice Cube, Tupac Shakur, and the Birth of West Coast Rap By Ben Westhoff

The History of Gangster Rap: From Schoolly D to Kendrick Lamar, the Rise of a Great American Art By Soren Baker

2pac vs. Biggie: An Illustrated History of Rap’s Greatest Battle by Jeff Weiss

The Dirty Version: On Stage, in the Studio, and in the Streets with Ol' Dirty Bastard By Buddha Monk

Enter The Wu-Tang: How Nine Men Changed Hip-Hop Forever: How Nine Men Changed Hip-Hop by OKP’s own “Spirit”

RAW: My Journey into the Wu-Tang by U-God

Sweat the Technique: Revelations on Creativity from the Lyrical Genius by Rakim

Black Noise - Tricia Rose