Exploring Planets in the Classroom http://www.soest.hawaii.edu/SPACEGRANT/class_acts/index.html Hands-on science activities from University of Hawaii. Mostly Planetary Science and Geology.
Live from Earth and Mars http://www-k12.atmos.washington.edu/k12/index.html More than just activities, also includes workshop materials and teacher/student projects.
Mars Exploration Curridulum http://marsnt3.jpl.nasa.gov/education/modules/webpages/curriculumwelcomepage.htm More activities about Mars
Reaching for the Red Planet http://lyra.colorado.edu/sbo/mary/redplanet.html Curriculum for grades 4-6.
Galileo Mission Education Modules http://www.jpl.nasa.gov/galileo/sepo/webflier.html Activites relating to Jupiter and it's moons.
Comet Recipe http://whyfiles.org/011comets/crecipe.html Make a comet in your classroom.
Space and Astronomy http://inspire.ospi.wednet.edu:8001/curric/space/index.html Lesson plans for all astronomy, but with most activities about the solar system.
Astronomy with a Stick http://www.nsta.org/programs/sst/aws/Default.htm Solar Astonomy
NASA/MSU-Bozeman CERES Project Educational Activities http://btc.montana.edu/ceres/html/EdActivities.html For grades K-12 following the NASA themes.
Infrared Activities http://www.ipac.caltech.edu/Outreach/Edu/activities.html List of Links to activies about the infrared part of the electromagnetic spectrum.