I picked up a copy of the Sears Catalogue circa 1897 when I was working on Lure. Now anytime I am looking for information on wagons, butter churns, etc. I have the perfect place to find a picture of one.
The How to Draw Manga Series. While some of the titles have a bit of drawing instruction, these are mostly design books. They have a book for every general manga subject: Robots, Occult, Ninjas or whatnot. The book on ninjas has information on sword fighting, throwing stars, the correct costuming, etc. I also like that certain moves are drawn in sequence.
The Big Blue Book of Grammar : this book is a very straight forward grammar rule book.
Thinkbabynames.com : This is my favorite site when I’m going to work on naming characters.
For my current project an epic fantasy novel with the working title of The Martlet, I am also using these websites.