This site from the Air and Space Museum (US) provides detailed information about our solar system, from early discovery to modern exploration tools. Find information about each planet and some ways to compare them.
This site is a 3-D environment full of real NASA mission data. Students can "explore the cosmos" from their computer. "Hop on an asteroid. Fly with NASA's Voyager 2 spacecraft. See the entire solar system moving in real time." (NASA description)
This NASA resource starts with an overview or definition of a planet. The In Depth section includes information about how this definition continues to evolve and how new discoveries inform the discussion.
This media-rich site provides information on each of planets of our solar system. Explore the videos and scroll down to find learn about the surface of each planet, as well as, statistics, size comparison and moons of each planet.