Windows to the Universe, from the University of Michigan, just seems to grow more and more incredible each month. Astronomy is a hook to interdisciplinary resources in the humanities. The summer edition of Science Scope, NSTA publication, is devoted to astronomy and the arts.
Sponsored by the National Earth Science Teachers Association (NESTA), this site provides a wide variety of resources about the Sun, Earth, Solar System, Space, Sciences, Culture, and People. There’s even a games section for students.