I collect field guides. There are some I love and some I don't love so much. If you're looking to buy a field guide, maybe this review will help you out.
These are just a bunch of fun. You use a dichotomous key as a step by step guide to figure out what species is in front of you. Each page asks you a question and tells you which page to go to based on your answer. They're kind of like a choose your own adventure, except real and with plants. The downside to dichotomous keys is they can make identification take a long time and they can be pretty confusing. I mean, how are you supposed to know how many needles a pine tree has in a bundle when the lowest branches of way above your head? Dichotomous keys are great in groups, especially with children, if you are in no rush to identify what lives along your trail.
These are by far my favorite field guides and for one single reason: they're durable. Hiking in the rain but still want to know what kind of salamander just wiggled through the mud? No problem. Plastic fold-outs are laminated and can survive rain. If you're anything like me, juggling a water bottle, binoculars, and a field guide may end with one of those items falling to the ground. But never fear with plastic fold-out guides; mud wipes right off. You can fold these guides down and slip them in your pocket, too. The only downside to these guides is they can be lacking information. A plastic fold-out may only show photographs of male birds during breeding season, which may not be so helpful when you see a couple of drab ducks on your creek walk. That being said, each field guide is specific to your location and what group of species you'll be identifying, so you won't need to flip through pages of birds you'll only see on the East Coast when you hike on the West Coast. Barnes & Nobles has a great collection of these laminated field guides and they're only about $7 each.
I seem to be building a collection of bird identification books. I don't tend to take these out with me as they are bulky and don't fair particularly well when dropped in mud, dirt, or water. They're also a pain to flip through when you need to quickly identify a migrating raptor. However, these guides are chock full of information including range, bird calls, and sometimes notes on behavior. I like to read these books at home before heading out and rely instead on a much lighter and durable plastic fold-out.
Create Your Own
Another option is to create your very own field guide. I created my own field guide for an assignment in my Field Biology class in high school, and I found it so helpful that I created another when counting migrating raptors in Yellowstone. All you need is a $1 small notebook from Walgreen's or any other store. Take it with you on your regular hike and draw or write what you see. You can even write some notes such as coloration, what they sound like, or what they were doing. Add a species name if you know it, or look it up online or in an identification guide when you get home. This notebook will be a personalized field guide to your location, only including the plants and animals that live in your area. You can keep it with you on hikes, and update it whenever you see something new. This will not only make it incredibly easy to find the species on future hikes, but will help you be able to identify species without needing a guide.