Nine Planets
http://seds.lpl.arizona.edu/nineplanets/nineplanets/
An overview of the history, mythology, and current scientific knowledge of each of the planets and moons in our solar system. Each page has text and images, some have sounds and movies, most provide references to additional related information
The Planetary Society
http://planetary.org/The Planetary Society is your connection to the exploration of the cosmos and the search for extraterrestrial life and intelligence discoveries, and more. For links to Leonids sites visit here. also try
Live! Leonids 98
http://sun-i.net/leo98/live/en/
SEDS
http://seds.lpl.arizona.edu/This is a site put together by students with a passion for space. There is just something for everyone here
Window on the Universe
http://www.windows.umich.edu/Fantastic textbook that covers all aspects of space and astronomy, from art and myths to scientific exploration and research
Picture of the Day
http://antwrp.gsfc.nasa.gov/apod/astropix.html
If you want to learn about space, bit by bit, visit this NASA site which gives a new picture and more info each day
The Exploratorium: Learning Centre
http://netra.exploratorium.edu/learning_studio/
Here not only do you learn about space, but a whole lot of other scientific disciplines. This site also details cute models or experiments that can be done at home.
Bradford Robotic Telescope Observatory
http://www.telescope.org/rti/index.html
So you want to know a little more about practical astronomy, give the Bradford Robotic Telescope a try. Not the most sophisticated site but very informative.
The Sun - A Multimedia Tour
http://www.astro.uva.nl/michielb/od95/
A favourite. If you ever read or sat in a lecture on the dynamic processes of our Sun, the different energy forms, the interplay between gravity and radiation. and understood very little or a lot but had no picture of what was happening. This site offers you a multimedia tour through video and audio files.
Astronomical Images Archive
http://www.stwing.upenn.edu/~jparker/astronomy/
And for all those pretty pictures. In addition to the pictures you can also get the basic astronomical info of the body you are looking at.
Skyview
http://skview.gsfc.nasa.gov/skyview.html
If you are fascinated by all those wavelengths which you cannot see visit Skyview. It gives you a new view on our universe.