Astronomical Society of the Pacific http://www.aspsky.org/education.html Home of Project ASTRO.
SSDOO Education Outreach Page http://ssdoo.gsfc.nasa.gov/education/education_home.html Launches, news and resources from the Space Science Data Operations Office of NASA/Goddard Space Flight Center.
Education Resources Catalog http://cass.jsc.nasa.gov/education/ERC/resources.html
NASA CORE http://core.nasa.gov/ Central Operation of Resources for Educators.
Challenger Center http://www.challenger.org/ Challenger Center for Space Science Education.
Students for the Exploration and Development of Space http://www.seds.org/
STScI Public Information http://oposite.stsci.edu/pubinfo/ Includes links to Hubble images.
NASA Quest http://quest.nasa.gov/space/teachers/liftoff/ Written guides to accompany the Liftoff to Learning video series.
LPI Education Resources http://www.lpi.usra.edu/education/education.html List of programs, products and resources from the Lunar and Planetary Institute.
NASA Spacelink http://spacelink.nasa.gov/.index.html An Aeronautics and Space Resource for Education.
Windows to the Universe http://www.windows.ucar.edu/ Web site about Earth and Space sciences. Ingludes games, art, data, and cool stuff.
SSI Education http://www.spacescience.org/Education/1.html Activities, information, and resources from the Space Science Institute.