A Field Guide to Birds of Eastern and Central North America, Roger Tory Peterson, Virginia Marie Peterson, Houghton Mifflin Company, Boston - If you only buy one field guide to carry into the field, this is the one to have. It is the classic by the master of birding, Roger Tory Peterson. The book is compact and fits into a large pocket. A must for any birder.
The Sibley Guide to Birds, David Allen Sibley - Probably the best and most complete source, this is considered by many to be the best field guide on birds of North America. The illustrations show many plummages, and are outstanding. Unfortunately, but book is a bit too large to fit into one's pocket for transporting into the field. Still, it is a superb reference.
National Geographic Field Guide to the Birds of North America, National Geographic, Washington, DC, ISBN 0-7922-7451-2, new edition. - This is the number two standard for field guides, and some prefer it over the Peterson's guide. It includes all birds of North American, so if you are traveling in one of the states that has eastern and western birds, you may want to take this one along. Some of the illustrations are superior to Peterson's and some are not as good.
Birds of North America, by Ken Kaufman - This is a good compact bird identification book that is small and light enough to take with you in the field.
Birds of North America, by Chandler Robbins, Bertel Bruun and Herbert S. Zim - This is another standard, with range maps located with the text and pictures of each bird.
Stokes Field Guide to Birds, (Eastern Region) by Donald and Lillian Stokes
The Sibley Guide to Bird Behavior is also an excellent book and a companion to The Sibley Guide to Birds.
Alabama Birds, by Thomas A. Imhof - Now deceased, he was Alabama's very own authority on Alabama Birds. The last edition was and may still be the most informative book on when and where birds have been seen in Alabama. There is also information on nesting and habits of birds in the state.
A Birder's Guide to Alabama, edited by John F. Porter, Jr. and dedicated to Thomas A. Imhof - This is the best book on places to go birding in Alabama, and how to get there.
The Alabama Coastal Birding Trail, published by the U.S. Fish & Wildlife Service - a good brochure on birding along the Alabama Gulf Coast.
Thanks to Bob Tate for providing many suggestions for birding books.
For a downloadable comprehensive list of suggested books and reference material click here.