The companion book for Love and Rockets is coming soon in August 2013.
It's going to be 240 pages and features in-depth interviews with creators Gilbert, Jaime and Mario Hernandez. There will be character family trees and glossary, timelines, the Hernandez Brothers bibliography of all things drawn over the 30 years.
You can download a 32-page preview from the link below (right-click, save as):
Definitely also check out The Art of Jaime Hernandez: The Secrets of Life and Death.