Best overviews: The Nine Planets Wikipedia
Best physical data and mission information: National Space Science Data Center
Best images: Hubble Space Telescope Keck II AO images of Io Photojournal Image Gallery at the Galileo Legacy Site PDS Map-a-planet
Official nomenclature: USGS Gazetteer of Planetary Nomenclature
Other Links: The Jupiter Ring System at the Planetary Rings Node Voyager Jupiter Science Summary
Check these sites for the most up-to-date facts on Jupiter’s small satellites. Scott Sheppard's Jupiter Satellite Page NASA's Solar System Dynamics pages: Satellite Properties and Satellite Elements