NASA’s MESSENGER mission to Mercury: messenger.jhuapl.edu
European Space Agency’s Venus Express mission: sci.esa.int/venusexpress
NASA’s visible Earth website with tons of great pictures of our planet: visibleearth.nasa.gov
NASA’s Lunar Reconnaissance Orbiter mission to the Moon (launches summer 2008): lunar.gsfc.nasa.gov
NASA’s Mars Exploration Rovers: marsrovers.nasa.gov/home/index.html
ESA’s Mars Express mission: www.esa.int/esaMI/Mars_Express/index.html
NASA’s Mars Reconnaissance Orbiter: mars.jpl.nasa/gov/mro/
NASA’s Galileo mission to Jupiter (completed 2003): galileo.jpl.nasa.gov
NASA’s Cassini mission to Saturn: saturn.jpl.nasa.gov
NASA’s Voyager 1 and 2 missions to Jupiter, Saturn, Uranus and Neptune and the edge of the Solar System: voyager.jpl.nasa.gov
NASA’s New Horizons mission to Pluto (currently en-route): pluto.jhuapl.edu
NASA Planetary Photojournal, filled with lots of pictures of the planets, their moons and their rings: photojournal.jpl.nasa.gov/index.html

Beyond the Solar System
Hubble Space Telescope, with lots of pictures of space: hubblesite.org
NASA Spitzer Space Telescope, an infrared telescope, with lots of pictures: www.spitzer.caltech.edu/
NASA Chandra X-ray Observatory: chandra.harvard.edu/