The MacBride Raptor Project is a good informational site with good pictures also. The selection is limited to hawks, falcons and owls, however.
The Raptor Center at the University of Minnesota has information pieces about many birds of prey. Good site to check out, it has a broad selection of species.
SERRC, which stands for the Southeastern Raptor Rehabilitation Center, has reports on a few of the raptors of the U.S. Their selection is a bit limited also, but their reports are very in depth.
The Breeding Bird Survey and Analysis, is a plethora of maps and pictures. The site has good maps and pictures of about every bird in the U.S., but not a lot of information is given.