Google Earth

(Credit: CNET Networks)

Ever since Google bought Keyhole's satellite software and merged it
with its own mapping software to create Google Earth, citizens of the
planet have been provided with amazing photos and valuable geographic
information. Start with a view of the entire planet, then manually zoom
into any country or city you like, or just type in a name of a
location. Version 4 added 3D models of real buildings and structures to
the program, and users can even create and submit their own using
Google Sketchup.

WorldWide Telescope

(Credit: CNET Networks)

While Google has the Earth's most excellent reference, Microsoft
takes the prize for information and imagery from across the universe.
The recently released and fabulous freeware WorldWide Telescope is the
most ambitious attempt to bring the power of massive space- and
ground-based telescopes onto your PC. Along with the incredible
pictures of black holes, nebulae, and radiation clouds, you can take
guided tours of celestial objects led by eminent astronomers and
educators.