Several non-profit and conservation oriented organizations publish a variety of field guides that narrow their focus either by region, topic, or both. Field guides can give you tons of information through illustrations and examples such as identifying edible or poisonous plants, types of geologic formations, species identification, and so much more. Though I've gone through my fair share of these handy books the two that I keep in my pack at all times are "The Sibley Guide to Birds of Western North America" by David Allen Sibley and the "Field Guide to the Rocky Mountain States" put out by the National Audubon Society. My junior year of college I took a very in depth ornithology class and found the Sibley's guide to be the most comprehensive and most fitting to the way I learn and identify birds but each guide has its pros and cons. As for my "Field Guide to the Rocky Mountain States", it was a Christmas present from my brother (another outdoor oriented Bennett) who knew a lot about the work I do and came with high praise. It covers pretty much everything found in the wildlands of Idaho, Montana, Wyoming, and Colorado. Over the years its gotten banged up and folded pages but still is so very useful in the field. Thank God for waterproof pages.
While these two books are indelible to me I do recommend that if you are seeking out a field guide (or several) for yourself that you find ones that are appropriate for what you do in the outdoors and the locale that you typically spend that time. Though they may share some common flora and fauna, a field guide for Northwest Montana isn't going to do you much good if you live in Southern Louisiana, or vis a versa. So when you are at your local book store or outdoor supply place be sure that you take your time and find what best suits you.
Come back to read tomorrow when I'll be discussing interactive online sources such as eNature.com, that help both novice and experienced wildlander alike learn and keep track of their observations in the field. Happy Reading!