I think that Microsoft has just surpassed Google in one discipline. WorldWide Telescope is better than Google Sky. The latter is included in Google Earth.
WWT website (nice presentation!)It works much like Google Earth/Sky but has many more textures in it and you can see many images that NASA folks are seeing via Chandra, Hubble, and other gadgets.
Download & install (direct link; don't be afraid to install DirectX 9, it won't destroy DirectX 10 on Vista)
My screenshot (there are better things to see)
A tour; how kids react
Get ready for all constellations, planets, moons, galaxies from Hubble, black holes, nebulae: everything you ever liked to see in the Cosmos. Guided tours are included. Thousands of pictures on their right locations.
The sky is not the only place where you can look at. In the lower left corner, there is "look at" and you may choose Sky, Earth, Panorama, or Planets. The Earth is a rough version of Google Earth - with a lower resolution but much better 3D realism. The Panorama shows rotatable pictures of Mars from the rovers' viewpoint while the Planets visualize many planets and moons, including the fractal planet Mandelbrot. ;-)
Another fun from Microsoft research: colorful barcodes. A new kind of filesystem has been designed for them. ;-) Click to learn more.
Finally, I guess that many people find most CAPTCHA (screwed letters and digits that you have to copy to prove that you are not a robot) too annoying and difficult - while they could be easy for computers. Assira is an alternative.
Believe me, I could make it work so that it tells you "you're human" when you succeed :-) but let's not waste too much time here.