The Frogman Auction Watch blog has a post on various G-Shock publication that have come out over the years. These magazine/books are referred to as mooks, and they are great for G-Shock reference and history. Most all of these have only been released in Japan, so most all the text is in Japanese. It's a nice overview of all the guides out there. Recent ones can be found on eBay.

Link

G-Shock Perfect Bible