This web link is an excellent source to
identify birds. All of the photos are
donated so the different species have
varying numbers of photos, but for some
you can get a fairly comprehensive view
of the typical and atypical specimens,
standard vs alternative plumage, adult
vs juvenile vs nestling variations.
http://nationalzoo.si.edu/ConservationAndScience/MigratoryBirds/Featured_Photo/default.cfm