For some time now, I've been studying how to build Earth in Blender. I've read quite a few tutorials, studied NASA's Blue Marble images, and received critique from other Blender enthusiasts. I now have some satisfactory results, which I'd be happy to share.
I've put together a 21-page tutorial which explains how I achieved my Earth renders. I know there are already a lot of Earth tutorials out there - but none that I found helped me get quite the effect that I wanted. My tutorial combines what I gleaned from all the other tutorials, with what I learned on my own through hours of experimenting. I'm sure it's not perfect - but I think it will be helpful for anyone interested in the subject.
The tutorial focuses on three different models of Earth - a photographic-style Earth, a Blue-Marble-style Earth, and a night Earth. It demonstrates how to render details such as proper specular shading and ray-traced cloud shadows.