What is the best book for moss ID. Preferably N. american. I would like a book that is similar to a picture type identification like the Audubon Society Pocket Guides
There really isn't a book that covers North America. There is a book that covers 50 of the most common mosses of PA.
Your best bet is to construct your own notebook using what you can find on the net. You can begin with the efloras treatment of bryophytes and tie in USDA images and Goggle for more info and images.