Downloads:

Free Monthly Sky Map
Free Stellarium sky software

Useful Websites:

Sky watching:
Astronomy Picture of the Day
Constellations
Google Earth & Sky
Eclipses
International Dark Sky Association
Messier Objects
Rensselaer's Hirsch Observatory
Sky & Telescope
Sky View
Starry Night

Observatories:
National Optical Astronomy Observatories
Cerro Tololo Inter-American Observatory
Kitt Peak National Observatory
Gemini Observatory
European Southern Observatory
National Solar Observatory
Anglo-Australian Observatory
Mauna Kea Observatories

Space Technology:
Hubble Space Telescope News
NASA
Space Telescope Science Institute
NASA Human Spaceflight
Visible Earth
Global Positioning System
SOHO

General Information:
Rensselaer Astrophysics Research
New York Center for Astrobiology
Universe Primer from U Michigan
Welcome to the Planets