eBird - A project of the Cornell Lab of Ornithology allowing birders to enter bird counts for use by scientists tracking population and migration trends. Also a great way to keep track of your life list, look up lists of birds recently observed at most public locations, and look at historical data from most public locations and other "hotspots."
The Feather Atlas - Promotes feather identification, research, and appreciation by providing high-resolution scans of the flight feathers of North American birds.