Imagine the Universe
The Imagine the Universe site includes educational resources for astrophysics topics:
Teachers' Corner - Lesson plans; Hera (Hera is an interface to software and data provided by the High Energy Astrophysics Science Archive Research Center at NASA/Goddard Space Flight Center. The data are from satellites which detect x-rays and gamma rays from objects such as black holes, neutron stars, galaxies, and supernovae.); posters and information/activity booklets; and other materials.
Resources Wiki: Browse and share astronomy resources which you and others have found useful.
Science: background information on astrophysics topics
Ask an Astrophysicist
Satellites and Data