University of Wisconsin
University of Wisconsin: The Constellations and Their Stars
An excellent site dedicated to the constellations and information about the objects which make them up. Contains a great deal of information about various stars, galaxies and other objects, as well as details on how best to observe them.
Other
Constellations Web Page: The Constellations
Information about 88 constellations, including the myths associated with them and details of the major astronomical objects that are part of them.