Field Guides
Here are a few to get you started, but there are hundreds more, on almost any subject you can imagine.
Check your library or bookstore.
Introduction and Method:
The
Amateur Naturalist's Handbook
Thoreau's Method: A Handbook for Nature Study
Plants:
The
Plant Observer's Guidebook: A Field Botany Manual for the Amateur Naturalist
Trees:
1001
Questions Answered About Trees
A Natural
History of Trees of Eastern and Central North America
Ponds/Wetlands:
Pond
Life: Revised and Updated (A Golden Guide from St. Martin's Press)
A Field
Guide to the Birds of Eastern and Central North America
The
National Audubon Society Field Guide to North American Reptiles and
Amphibians
A Field
Guide to Wildflowers : Northeastern and North-Central North America
(Peterson Field Guides)