A couple of weeks ago Microsoft launched it's Worldwide Telescope which is really cool. I was playing about with it with my kids and they thought it was great.
For those of you who wonder the center of the milky way looks like this

Yesterday Google kept up the pressure and launched it's Google Earth API at it's I/O conference in San Francisco.
Another really cool app even though there seem to be a couple of issues with the page when in Firefox.

Tags: Google Earth API Microsoft Worldwide Telescope