I never go out unless I have a book with me. Its saved my ass a couple of times.
I think these guys make one for a lot of different regions in the world. $15 bucks is a small price to pay to not get sick, or worse yet, die.
Here is the book I use. Small, easy to carry and great pictures with details on each mushroom along with false varietys linked to them and how to distinguish.
Mushrooms of the Upper Midwest: A Simple Guide to Common Mushrooms: Teresa Marrone, Kathy Yerich: 9781591934172: Amazon.com: Books