A chart showing illustrations of select North American birds is available on the National Audubon Society's Guide to North American Birds webpage. Charts comparing physical features between birds to aid in identification are available from the website of the Cornell Lab of Ornithology.
The National Audubon Society's bird identification chart also provides sound clips of each species' song or call. You can click on individual entries to see physical description, behavior and range.
Comparative charts from the Cornell Lab of Ornithology compare relative bird sizes, while other charts identify bird anatomical features relevant to identification, such as eye stripes, wing bars and throat patches.