Discovery School's Astronomy & Space - While this space is titled "Astronomy & Space", it also contains significant information on the exploration of Mars. I've chosen to put the site here because it has wonderful content from the Hubble Telescope. The images are wonderful for exploration and familiarizing students with the great unknowns in space. Unfortunately, the Discovery Channel chooses to use "pop-up" advertising, so you will want to be aware of this and possibly use a pop-up blocker.

Science @ NASA - Images, streaming audio, videos, and links to space exploration project sites at various universities and agencies make this a useful resource. With both interactive content and resource content, a student (or teacher) can gleen a lot of information about astronomy from this site and it's extensions. It is easy to wander away from this site though, so opening links using the "open in new window" option is helpful.

Sky and Telescope's Interactive Sky Chart - Enter your location, or any other location, and see what the night sky will look like there! While the Interactive Sky Chart is the most fun, there is also a lot of educational content on this site. Based upon Sky and Telescope Magazine, the content is article oriented and better for exploration learning rather than for seeking specific information on a specific topic.

NOVA Online - PBS's popular science series has its own space exploration site. Learn about Supernovas, the history of the Universe (Big Bang Theory), galaxies and more. PBS provides interactive Flash presentations linked from a text based site. You don't have to have FLASH to benefit from the site, but you will need it to view the dynamic presentations.

Astronomy for Kids - One of the few "personal" sites I've linked to, this site provides tons of great basic content about astronomy. Built through a passion for astronomy, the visual and written content is of high quality and is one of the best starting places for kids. I enjoyed reading through the site myself. There aren't a lot of high tech elements, but the content is solid.