There are a few decent field guides out there to help you with id but I also just came across this neat App by Audubon and thought I’d pass it along. Just go to the “marketplace” on your device and do a search to check it out. Or visit their website.
You can get the mushroom app for the iPhone, iPad and Android platforms:
Get in touch with your inner Mycologist and own the most comprehensive and accurate guide to North American mushrooms and other fungi available to date. Search over 550 common species, each with professional photographs and detailed descriptions.