Observing

Heavens above. Where and when to see satellites: http://www.heavens-above.com/

Astronomy Resources

UK Supplier of Telescopes since 1785:
http://www.telescopehouse.com/

Ian King imaging supplies
http://www.iankingimaging.com/

Astronomy prints of Hubble and Mars Hirise images:
www.astronomyimages.co.uk

Spaceflight

Encyclopedia Astronautica. An unbelievably well-researched and complete encyclopedia of spacecraft:
http://www.astronautix.com/

Space Technology: How does all this outer space stuff work?
http://www.braeunig.us/space/index.htm 

Apollo archive. Images and much more about the Apollo missions:
http://www.apolloarchive.com/apollo_gallery.html

NASA images:
http://www.nasaimages.org/

Atomic Rockets. This is a really cool site: http://www.projectrho.com/rocket/index.html

The Moon landings were real!
http://www.clavius.org/