Hubblesite.org is the official site of the Hubble Space Telescope or HST. Thousands of images from the Solar System and deep space, Hubble's discoveries, space missions, videos, news etc.

Astronomy.com is the website of 'Astronomy Magazine' and has a huge amount of information... Intro to the skies, Understanding the Solar System, Star atlas, Glossary, Calendar of events, Telescope info, Wallpapers.

Nasa.gov. A massive site. Images, News, Missions, The Shuttle & ISS, Satellites, Moon, Solar System, Universe, Technology, Calendar of events, NASA's history.

StarrySkies.com answers all sorts of questions.

Derek Haselden's Astronomical Tables for literally hundreds of astronomical phenomena.

Heavens-above.com predict the appearance of numerous satellites. Times, positions & durations.

Spacetelescope.org. Lots of stunning images, News, Videos, Info on the HST, Science.

ScienceDaily.com/Astronomy. Your source for the latest research, news, discoveries and breakthroughs in astronomy.

Apod.nasa.gov. NASA's astronomy picture of the day. Has a massive archive of images.

David Darling's Encyclopedia of Science. A phenomenal amount of information on scientific subjects, including astronomy. Clearly explained.

Sky & Telescope Magazine news page. All the latest astronomy news.