Let me count the ways

There are already a number of freeware/commercial software out there which can render a 3D Earth for people to explore and enjoy. The few major ones I've come across are:

1. Google Earth

Google Earth is fun, interactive and photographic, but the imagery is segmented.

2. Celestia

How good Celestia looks depends on the textures you feed it

3. NASA's World Wind

Started by NASA, World Wind is an open source project. Great for visualizing data

While these software render the Earth using real-world satellite data (such as the BMNG dataset) and can look quite detailed, none of them come close to how things actually look from space. Naturally, as I haven't been to space myself, I can only imagine what it is like based on my research of Earth documentaries and imagery released by astronauts and space agencies such as NASA and ESA.

Ultimately, my goal is to be able to render realistic views of a CG Earth that closely match actual views from space. A fun challenge indeed ^^