JPL's Welcome to the Planets is a collection of the best 200 images from 20 years of NASA planetary exploration. Each image is accompanied by information about solar-system bodies and various spacecraft that explored them. Designed as an interactive introduction to planetary exploration using images and text. "Welcome to the Planets" provides information about the spacecraft that acquired the data, along with information about each planet.
Solar-System Browser contains a planetary-data repository from the U.S. Geological Survey. Click on the large graphic that depicts all the major bodies in the solar system, and you'll be presented with the physical characteristics of any object you selected.