A thorough introduction to orbital mechanics, spacecraft project design, and flight operations, all easily understandable by the general public and students. You'll almost be ready to work in Mission Control after reading this!

http://www.jpl.nasa.gov/basics/

Billed as the world's first online virtual planetarium, this site creates a "never-ending" planetarium show on the Web with a combination of static and animated images as well as supporting text. There's also a separate archive of space images, a gift shop, and images taken during a very recent observing trip to Mauna Kea, Hawaii.

http://ucsu.colorado.edu/~peterscc/Home.html

The SKYLON project is a private British effort to build a spaceplane that can carry up to 12 tons of cargo into orbit. This unmanned vehicle would talk about 10 years to develop. There's historical and current news and research info, although the link to the site can be very slow at times, making it difficult to read these sections.

http://www.gbnet.net/orgs/skylon/