The Book of Griswold & Wagner Favorite Wapak Sidney Hollow Ware(Blue Book because it has a blue cover), I think the latest is the 5th edition.
The Book of Wagner & Griswold Martin Lodge Vollrath Excelsior(red book because it has a red cover)
There is also a yellow book which I believe has a lot of Gem and Muffin pans.
All published by Schiffer and yes I believe available on Amazon and other outlets
You will see all 3 shown on the below link
https://www.amazon.com/Griswold-Muffin-Pans-Schiffer-Collectors/dp/0764302396Shop around you may find them less than at Amazon
They are great reference material, as for actual value of the pieces i generally scan ebay for sold listings and other auction sites to get an estimate on what the market trend is.
I like books
I just got The Red Book No.11 The collectors guide to old fruit jars for Christmas...If you think collecting cast iron is crazy fruit jars will have your head spinning :o